allow building a kernel without buffer_heads

allow building a kernel without buffer_heads

[Christoph Hellwig]

Hi all,

This series allows to build a kernel without buffer_heads, which I
think is useful to show where the dependencies are, and maybe also
for some very much limited environments, where people just needs
xfs and/or btrfs and some of the read-only block based file systems.

It first switches buffered writes (but not writeback) for block devices
to use iomap unconditionally, but still using buffer_heads, and then
adds a CONFIG_BUFFER_HEAD selected by all file systems that need it
(which is most block based file systems), makes the buffer_head support
in iomap optional, and adds an alternative implementation of the block
device address_operations using iomap.  This latter implementation
will also be useful to support block size > PAGE_SIZE for block device
nodes as buffer_heads won't work very well for that.

Note that for now the md software raid drivers is also disabled as it has
some (rather questionable) buffer_head usage in the unconditionally built
bitmap code.  I have a series pending to make the bitmap code conditional
and deprecated it, but it hasn't been merged yet.

Changes since v1:
 - drop the already merged prep patches
 - depend on FS_IOMAP not IOMAP
 - pick a better new name for block_page_mkwrite_return

[PATCH 1/6] fs: remove emergency_thaw_bdev

[Christoph Hellwig]

Fold emergency_thaw_bdev into it's only caller, to prepare for buffer.c
to be built only when buffer_head support is enabled.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 fs/buffer.c   | 6 ------
 fs/internal.h | 6 ------
 fs/super.c    | 4 +++-
 3 files changed, 3 insertions(+), 13 deletions(-)

diff --git a/fs/buffer.c b/fs/buffer.c
index bd091329026c0f..376f468e16662d 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -562,12 +562,6 @@ static int osync_buffers_list(spinlock_t *lock, struct list_head *list)
 	return err;
 }
 
-void emergency_thaw_bdev(struct super_block *sb)
-{
-	while (sb->s_bdev && !thaw_bdev(sb->s_bdev))
-		printk(KERN_WARNING "Emergency Thaw on %pg\n", sb->s_bdev);
-}
-
 /**
  * sync_mapping_buffers - write out & wait upon a mapping's "associated" buffers
  * @mapping: the mapping which wants those buffers written
diff --git a/fs/internal.h b/fs/internal.h
index f7a3dc11102647..d538d832fd608b 100644
--- a/fs/internal.h
+++ b/fs/internal.h
@@ -23,16 +23,10 @@ struct mnt_idmap;
  */
 #ifdef CONFIG_BLOCK
 extern void __init bdev_cache_init(void);
-
-void emergency_thaw_bdev(struct super_block *sb);
 #else
 static inline void bdev_cache_init(void)
 {
 }
-static inline int emergency_thaw_bdev(struct super_block *sb)
-{
-	return 0;
-}
 #endif /* CONFIG_BLOCK */
 
 /*
diff --git a/fs/super.c b/fs/super.c
index e781226e28800c..bc666e7ee1a984 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -1029,7 +1029,9 @@ static void do_thaw_all_callback(struct super_block *sb)
 {
 	down_write(&sb->s_umount);
 	if (sb->s_root && sb->s_flags & SB_BORN) {
-		emergency_thaw_bdev(sb);
+		if (IS_ENABLED(CONFIG_BLOCK))
+			while (sb->s_bdev && !thaw_bdev(sb->s_bdev))
+				pr_warn("Emergency Thaw on %pg\n", sb->s_bdev);
 		thaw_super_locked(sb);
 	} else {
 		up_write(&sb->s_umount);
-- 
2.39.2

Re: [PATCH 1/6] fs: remove emergency_thaw_bdev

[Johannes Thumshirn]

Looks good,
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>

Re: [PATCH 1/6] fs: remove emergency_thaw_bdev

[Hannes Reinecke]

On 7/20/23 16:04, Christoph Hellwig wrote:
> Fold emergency_thaw_bdev into it's only caller, to prepare for buffer.c
> to be built only when buffer_head support is enabled.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>   fs/buffer.c   | 6 ------
>   fs/internal.h | 6 ------
>   fs/super.c    | 4 +++-
>   3 files changed, 3 insertions(+), 13 deletions(-)
> 
Reviewed-by: Hannes Reinecke <hare@suse.de>

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                Kernel Storage Architect
hare@suse.de                              +49 911 74053 688
SUSE Software Solutions GmbH, Maxfeldstr. 5, 90409 Nürnberg
HRB 36809 (AG Nürnberg), Geschäftsführer: Ivo Totev, Andrew
Myers, Andrew McDonald, Martje Boudien Moerman

Re: [PATCH 1/6] fs: remove emergency_thaw_bdev

[Luis Chamberlain]

On Thu, Jul 20, 2023 at 04:04:47PM +0200, Christoph Hellwig wrote:
> Fold emergency_thaw_bdev into it's only caller, to prepare for buffer.c
> to be built only when buffer_head support is enabled.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>

Reviewed-by: Luis Chamberlain <mcgrof@kernel.org>

  Luis

[PATCH 2/6] fs: rename and move block_page_mkwrite_return

[Christoph Hellwig]

block_page_mkwrite_return is neither block nor mkwrite specific, and
should not be under CONFIG_BLOCK.  Move it to mm.h and rename it to
vmf_fs_error.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 fs/ext4/inode.c             |  2 +-
 fs/f2fs/file.c              |  2 +-
 fs/gfs2/file.c              | 16 ++++++++--------
 fs/iomap/buffered-io.c      |  2 +-
 fs/nilfs2/file.c            |  2 +-
 fs/udf/file.c               |  2 +-
 include/linux/buffer_head.h | 12 ------------
 include/linux/mm.h          | 18 ++++++++++++++++++
 8 files changed, 31 insertions(+), 25 deletions(-)

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 43775a6ca5054a..6eea0886b88553 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -6140,7 +6140,7 @@ vm_fault_t ext4_page_mkwrite(struct vm_fault *vmf)
 	if (err == -ENOSPC && ext4_should_retry_alloc(inode->i_sb, &retries))
 		goto retry_alloc;
 out_ret:
-	ret = block_page_mkwrite_return(err);
+	ret = vmf_fs_error(err);
 out:
 	filemap_invalidate_unlock_shared(mapping);
 	sb_end_pagefault(inode->i_sb);
diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
index 093039dee99206..9b3871fb9bfc44 100644
--- a/fs/f2fs/file.c
+++ b/fs/f2fs/file.c
@@ -159,7 +159,7 @@ static vm_fault_t f2fs_vm_page_mkwrite(struct vm_fault *vmf)
 
 	sb_end_pagefault(inode->i_sb);
 err:
-	return block_page_mkwrite_return(err);
+	return vmf_fs_error(err);
 }
 
 static const struct vm_operations_struct f2fs_file_vm_ops = {
diff --git a/fs/gfs2/file.c b/fs/gfs2/file.c
index 1bf3c4453516f2..897ef62d6d77a7 100644
--- a/fs/gfs2/file.c
+++ b/fs/gfs2/file.c
@@ -432,7 +432,7 @@ static vm_fault_t gfs2_page_mkwrite(struct vm_fault *vmf)
 	gfs2_holder_init(ip->i_gl, LM_ST_EXCLUSIVE, 0, &gh);
 	err = gfs2_glock_nq(&gh);
 	if (err) {
-		ret = block_page_mkwrite_return(err);
+		ret = vmf_fs_error(err);
 		goto out_uninit;
 	}
 
@@ -474,7 +474,7 @@ static vm_fault_t gfs2_page_mkwrite(struct vm_fault *vmf)
 
 	err = gfs2_rindex_update(sdp);
 	if (err) {
-		ret = block_page_mkwrite_return(err);
+		ret = vmf_fs_error(err);
 		goto out_unlock;
 	}
 
@@ -482,12 +482,12 @@ static vm_fault_t gfs2_page_mkwrite(struct vm_fault *vmf)
 	ap.target = data_blocks + ind_blocks;
 	err = gfs2_quota_lock_check(ip, &ap);
 	if (err) {
-		ret = block_page_mkwrite_return(err);
+		ret = vmf_fs_error(err);
 		goto out_unlock;
 	}
 	err = gfs2_inplace_reserve(ip, &ap);
 	if (err) {
-		ret = block_page_mkwrite_return(err);
+		ret = vmf_fs_error(err);
 		goto out_quota_unlock;
 	}
 
@@ -500,7 +500,7 @@ static vm_fault_t gfs2_page_mkwrite(struct vm_fault *vmf)
 	}
 	err = gfs2_trans_begin(sdp, rblocks, 0);
 	if (err) {
-		ret = block_page_mkwrite_return(err);
+		ret = vmf_fs_error(err);
 		goto out_trans_fail;
 	}
 
@@ -508,7 +508,7 @@ static vm_fault_t gfs2_page_mkwrite(struct vm_fault *vmf)
 	if (gfs2_is_stuffed(ip)) {
 		err = gfs2_unstuff_dinode(ip);
 		if (err) {
-			ret = block_page_mkwrite_return(err);
+			ret = vmf_fs_error(err);
 			goto out_trans_end;
 		}
 	}
@@ -524,7 +524,7 @@ static vm_fault_t gfs2_page_mkwrite(struct vm_fault *vmf)
 
 	err = gfs2_allocate_page_backing(page, length);
 	if (err)
-		ret = block_page_mkwrite_return(err);
+		ret = vmf_fs_error(err);
 
 out_page_locked:
 	if (ret != VM_FAULT_LOCKED)
@@ -558,7 +558,7 @@ static vm_fault_t gfs2_fault(struct vm_fault *vmf)
 	gfs2_holder_init(ip->i_gl, LM_ST_SHARED, 0, &gh);
 	err = gfs2_glock_nq(&gh);
 	if (err) {
-		ret = block_page_mkwrite_return(err);
+		ret = vmf_fs_error(err);
 		goto out_uninit;
 	}
 	ret = filemap_fault(vmf);
diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index adb92cdb24b009..0607790827b48a 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -1286,7 +1286,7 @@ vm_fault_t iomap_page_mkwrite(struct vm_fault *vmf, const struct iomap_ops *ops)
 	return VM_FAULT_LOCKED;
 out_unlock:
 	folio_unlock(folio);
-	return block_page_mkwrite_return(ret);
+	return vmf_fs_error(ret);
 }
 EXPORT_SYMBOL_GPL(iomap_page_mkwrite);
 
diff --git a/fs/nilfs2/file.c b/fs/nilfs2/file.c
index a9eb3487efb2c2..740ce26d1e7657 100644
--- a/fs/nilfs2/file.c
+++ b/fs/nilfs2/file.c
@@ -108,7 +108,7 @@ static vm_fault_t nilfs_page_mkwrite(struct vm_fault *vmf)
 	wait_for_stable_page(page);
  out:
 	sb_end_pagefault(inode->i_sb);
-	return block_page_mkwrite_return(ret);
+	return vmf_fs_error(ret);
 }
 
 static const struct vm_operations_struct nilfs_file_vm_ops = {
diff --git a/fs/udf/file.c b/fs/udf/file.c
index 243840dc83addf..c0e2080e639eec 100644
--- a/fs/udf/file.c
+++ b/fs/udf/file.c
@@ -67,7 +67,7 @@ static vm_fault_t udf_page_mkwrite(struct vm_fault *vmf)
 		err = block_commit_write(page, 0, end);
 	if (err < 0) {
 		unlock_page(page);
-		ret = block_page_mkwrite_return(err);
+		ret = vmf_fs_error(err);
 		goto out_unlock;
 	}
 out_dirty:
diff --git a/include/linux/buffer_head.h b/include/linux/buffer_head.h
index 6cb3e9af78c9ed..7002a9ff63a3da 100644
--- a/include/linux/buffer_head.h
+++ b/include/linux/buffer_head.h
@@ -291,18 +291,6 @@ int generic_cont_expand_simple(struct inode *inode, loff_t size);
 int block_commit_write(struct page *page, unsigned from, unsigned to);
 int block_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf,
 				get_block_t get_block);
-/* Convert errno to return value from ->page_mkwrite() call */
-static inline vm_fault_t block_page_mkwrite_return(int err)
-{
-	if (err == 0)
-		return VM_FAULT_LOCKED;
-	if (err == -EFAULT || err == -EAGAIN)
-		return VM_FAULT_NOPAGE;
-	if (err == -ENOMEM)
-		return VM_FAULT_OOM;
-	/* -ENOSPC, -EDQUOT, -EIO ... */
-	return VM_FAULT_SIGBUS;
-}
 sector_t generic_block_bmap(struct address_space *, sector_t, get_block_t *);
 int block_truncate_page(struct address_space *, loff_t, get_block_t *);
 
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 2dd73e4f3d8e3a..75777eae1c9c26 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -3386,6 +3386,24 @@ static inline vm_fault_t vmf_error(int err)
 	return VM_FAULT_SIGBUS;
 }
 
+/*
+ * Convert errno to return value for ->page_mkwrite() calls.
+ *
+ * This should eventually be merged with vmf_error() above, but will need a
+ * careful audit of all vmf_error() callers.
+ */
+static inline vm_fault_t vmf_fs_error(int err)
+{
+	if (err == 0)
+		return VM_FAULT_LOCKED;
+	if (err == -EFAULT || err == -EAGAIN)
+		return VM_FAULT_NOPAGE;
+	if (err == -ENOMEM)
+		return VM_FAULT_OOM;
+	/* -ENOSPC, -EDQUOT, -EIO ... */
+	return VM_FAULT_SIGBUS;
+}
+
 struct page *follow_page(struct vm_area_struct *vma, unsigned long address,
 			 unsigned int foll_flags);
 
-- 
2.39.2

Re: [PATCH 2/6] fs: rename and move block_page_mkwrite_return

[Johannes Thumshirn]

Looks good,
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>

Re: [PATCH 2/6] fs: rename and move block_page_mkwrite_return

[Hannes Reinecke]

On 7/20/23 16:04, Christoph Hellwig wrote:
> block_page_mkwrite_return is neither block nor mkwrite specific, and
> should not be under CONFIG_BLOCK.  Move it to mm.h and rename it to
> vmf_fs_error.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>   fs/ext4/inode.c             |  2 +-
>   fs/f2fs/file.c              |  2 +-
>   fs/gfs2/file.c              | 16 ++++++++--------
>   fs/iomap/buffered-io.c      |  2 +-
>   fs/nilfs2/file.c            |  2 +-
>   fs/udf/file.c               |  2 +-
>   include/linux/buffer_head.h | 12 ------------
>   include/linux/mm.h          | 18 ++++++++++++++++++
>   8 files changed, 31 insertions(+), 25 deletions(-)
> 
Reviewed-by: Hannes Reinecke <hare@suse.de>

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                Kernel Storage Architect
hare@suse.de                              +49 911 74053 688
SUSE Software Solutions GmbH, Maxfeldstr. 5, 90409 Nürnberg
HRB 36809 (AG Nürnberg), Geschäftsführer: Ivo Totev, Andrew
Myers, Andrew McDonald, Martje Boudien Moerman

Re: [PATCH 2/6] fs: rename and move block_page_mkwrite_return

[Luis Chamberlain]

On Thu, Jul 20, 2023 at 04:04:48PM +0200, Christoph Hellwig wrote:
> block_page_mkwrite_return is neither block nor mkwrite specific, and
> should not be under CONFIG_BLOCK.  Move it to mm.h and rename it to
> vmf_fs_error.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>

Reviewed-by: Luis Chamberlain <mcgrof@kernel.org>

 Luis

[PATCH 3/6] block: open code __generic_file_write_iter for blkdev writes

[Christoph Hellwig]

Open code __generic_file_write_iter to remove the indirect call into
->direct_IO and to prepare using the iomap based write code.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 block/fops.c | 44 ++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 42 insertions(+), 2 deletions(-)

diff --git a/block/fops.c b/block/fops.c
index a286bf3325c5d8..eb599a173ef02d 100644
--- a/block/fops.c
+++ b/block/fops.c
@@ -533,6 +533,29 @@ static int blkdev_release(struct inode *inode, struct file *filp)
 	return 0;
 }
 
+static ssize_t
+blkdev_direct_write(struct kiocb *iocb, struct iov_iter *from)
+{
+	size_t count = iov_iter_count(from);
+	ssize_t written;
+
+	written = kiocb_invalidate_pages(iocb, count);
+	if (written) {
+		if (written == -EBUSY)
+			return 0;
+		return written;
+	}
+
+	written = blkdev_direct_IO(iocb, from);
+	if (written > 0) {
+		kiocb_invalidate_post_direct_write(iocb, count);
+		iocb->ki_pos += written;
+	}
+	if (written != -EIOCBQUEUED)
+		iov_iter_revert(from, count - written - iov_iter_count(from));
+	return written;
+}
+
 /*
  * Write data to the block device.  Only intended for the block device itself
  * and the raw driver which basically is a fake block device.
@@ -542,7 +565,8 @@ static int blkdev_release(struct inode *inode, struct file *filp)
  */
 static ssize_t blkdev_write_iter(struct kiocb *iocb, struct iov_iter *from)
 {
-	struct block_device *bdev = I_BDEV(iocb->ki_filp->f_mapping->host);
+	struct file *file = iocb->ki_filp;
+	struct block_device *bdev = I_BDEV(file->f_mapping->host);
 	struct inode *bd_inode = bdev->bd_inode;
 	loff_t size = bdev_nr_bytes(bdev);
 	size_t shorted = 0;
@@ -569,7 +593,23 @@ static ssize_t blkdev_write_iter(struct kiocb *iocb, struct iov_iter *from)
 		iov_iter_truncate(from, size);
 	}
 
-	ret = __generic_file_write_iter(iocb, from);
+	ret = file_remove_privs(file);
+	if (ret)
+		return ret;
+
+	ret = file_update_time(file);
+	if (ret)
+		return ret;
+
+	if (iocb->ki_flags & IOCB_DIRECT) {
+		ret = blkdev_direct_write(iocb, from);
+		if (ret >= 0 && iov_iter_count(from))
+			ret = direct_write_fallback(iocb, from, ret,
+					generic_perform_write(iocb, from));
+	} else {
+		ret = generic_perform_write(iocb, from);
+	}
+
 	if (ret > 0)
 		ret = generic_write_sync(iocb, ret);
 	iov_iter_reexpand(from, iov_iter_count(from) + shorted);
-- 
2.39.2

Re: [PATCH 3/6] block: open code __generic_file_write_iter for blkdev writes

[Johannes Thumshirn]

Looks good,
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>

Re: [PATCH 3/6] block: open code __generic_file_write_iter for blkdev writes

[Hannes Reinecke]

On 7/20/23 16:04, Christoph Hellwig wrote:
> Open code __generic_file_write_iter to remove the indirect call into
> ->direct_IO and to prepare using the iomap based write code.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>   block/fops.c | 44 ++++++++++++++++++++++++++++++++++++++++++--
>   1 file changed, 42 insertions(+), 2 deletions(-)
> 
Reviewed-by: Hannes Reinecke <hare@suse.de>

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                Kernel Storage Architect
hare@suse.de                              +49 911 74053 688
SUSE Software Solutions GmbH, Maxfeldstr. 5, 90409 Nürnberg
HRB 36809 (AG Nürnberg), Geschäftsführer: Ivo Totev, Andrew
Myers, Andrew McDonald, Martje Boudien Moerman

Re: [PATCH 3/6] block: open code __generic_file_write_iter for blkdev writes

[Luis Chamberlain]

On Thu, Jul 20, 2023 at 04:04:49PM +0200, Christoph Hellwig wrote:
> Open code __generic_file_write_iter to remove the indirect call into
> ->direct_IO and to prepare using the iomap based write code.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  block/fops.c | 44 ++++++++++++++++++++++++++++++++++++++++++--
>  1 file changed, 42 insertions(+), 2 deletions(-)
> 
> diff --git a/block/fops.c b/block/fops.c
> index a286bf3325c5d8..eb599a173ef02d 100644
> --- a/block/fops.c
> +++ b/block/fops.c
> @@ -533,6 +533,29 @@ static int blkdev_release(struct inode *inode, struct file *filp)
>  	return 0;
>  }
>  
> +static ssize_t
> +blkdev_direct_write(struct kiocb *iocb, struct iov_iter *from)
> +{
> +	size_t count = iov_iter_count(from);
> +	ssize_t written;
> +
> +	written = kiocb_invalidate_pages(iocb, count);
> +	if (written) {
> +		if (written == -EBUSY)
> +			return 0;
> +		return written;
> +	}
> +
> +	written = blkdev_direct_IO(iocb, from);
> +	if (written > 0) {
> +		kiocb_invalidate_post_direct_write(iocb, count);
> +		iocb->ki_pos += written;
> +	}

I noted in the last series how this could be negative and then crash:

https://lkml.kernel.org/r/ZG6OTWckNlz+P+mo@bombadil.infradead.org

This can be fixed as follows:

diff --git a/block/fops.c b/block/fops.c
index eb599a173ef0..936ed207b5dc 100644
--- a/block/fops.c
+++ b/block/fops.c
@@ -536,9 +536,13 @@ static int blkdev_release(struct inode *inode, struct file *filp)
 static ssize_t
 blkdev_direct_write(struct kiocb *iocb, struct iov_iter *from)
 {
+	struct block_device *bdev = I_BDEV(iocb->ki_filp->f_mapping->host);
 	size_t count = iov_iter_count(from);
 	ssize_t written;
 
+	if (blkdev_dio_unaligned(bdev, iocb->ki_pos, from))
+                return -EINVAL;
+
 	written = kiocb_invalidate_pages(iocb, count);
 	if (written) {
 		if (written == -EBUSY)

With that:

Reviewed-by: Luis Chamberlain <mcgrof@kernel.org>

  Luis

[PATCH 4/6] block: stop setting ->direct_IO

[Christoph Hellwig]

Direct I/O on block devices now nevers goes through aops->direct_IO.
Stop setting it and set the FMODE_CAN_ODIRECT in ->open instead.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 block/fops.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/block/fops.c b/block/fops.c
index eb599a173ef02d..0c37c35003c3b7 100644
--- a/block/fops.c
+++ b/block/fops.c
@@ -428,7 +428,6 @@ const struct address_space_operations def_blk_aops = {
 	.writepage	= blkdev_writepage,
 	.write_begin	= blkdev_write_begin,
 	.write_end	= blkdev_write_end,
-	.direct_IO	= blkdev_direct_IO,
 	.migrate_folio	= buffer_migrate_folio_norefs,
 	.is_dirty_writeback = buffer_check_dirty_writeback,
 };
@@ -505,7 +504,7 @@ static int blkdev_open(struct inode *inode, struct file *filp)
 	 * during an unstable branch.
 	 */
 	filp->f_flags |= O_LARGEFILE;
-	filp->f_mode |= FMODE_BUF_RASYNC;
+	filp->f_mode |= FMODE_BUF_RASYNC | FMODE_CAN_ODIRECT;
 
 	/*
 	 * Use the file private data to store the holder for exclusive openes.
-- 
2.39.2

Re: [PATCH 4/6] block: stop setting ->direct_IO

[Johannes Thumshirn]

Looks good,
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>

Re: [PATCH 4/6] block: stop setting ->direct_IO

[Hannes Reinecke]

On 7/20/23 16:04, Christoph Hellwig wrote:
> Direct I/O on block devices now nevers goes through aops->direct_IO.
> Stop setting it and set the FMODE_CAN_ODIRECT in ->open instead.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>   block/fops.c | 3 +--
>   1 file changed, 1 insertion(+), 2 deletions(-)
> 
Reviewed-by: Hannes Reinecke <hare@suse.de>

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                Kernel Storage Architect
hare@suse.de                              +49 911 74053 688
SUSE Software Solutions GmbH, Maxfeldstr. 5, 90409 Nürnberg
HRB 36809 (AG Nürnberg), Geschäftsführer: Ivo Totev, Andrew
Myers, Andrew McDonald, Martje Boudien Moerman

Re: [PATCH 4/6] block: stop setting ->direct_IO

[Luis Chamberlain]

On Thu, Jul 20, 2023 at 04:04:50PM +0200, Christoph Hellwig wrote:
> Direct I/O on block devices now nevers goes through aops->direct_IO.
> Stop setting it and set the FMODE_CAN_ODIRECT in ->open instead.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>

Reviewed-by: Luis Chamberlain <mcgrof@kernel.org>

  Luis

[PATCH 5/6] block: use iomap for writes to block devices

[Christoph Hellwig]

Use iomap in buffer_head compat mode to write to block devices.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 block/Kconfig |  1 +
 block/fops.c  | 31 +++++++++++++++++++++++++++++--
 2 files changed, 30 insertions(+), 2 deletions(-)

diff --git a/block/Kconfig b/block/Kconfig
index 86122e459fe046..1a13ef0b1ca10c 100644
--- a/block/Kconfig
+++ b/block/Kconfig
@@ -5,6 +5,7 @@
 menuconfig BLOCK
        bool "Enable the block layer" if EXPERT
        default y
+       select FS_IOMAP
        select SBITMAP
        help
 	 Provide block layer support for the kernel.
diff --git a/block/fops.c b/block/fops.c
index 0c37c35003c3b7..31d356c83f27a3 100644
--- a/block/fops.c
+++ b/block/fops.c
@@ -15,6 +15,7 @@
 #include <linux/falloc.h>
 #include <linux/suspend.h>
 #include <linux/fs.h>
+#include <linux/iomap.h>
 #include <linux/module.h>
 #include "blk.h"
 
@@ -386,6 +387,27 @@ static ssize_t blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter)
 	return __blkdev_direct_IO(iocb, iter, bio_max_segs(nr_pages));
 }
 
+static int blkdev_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
+		unsigned int flags, struct iomap *iomap, struct iomap *srcmap)
+{
+	struct block_device *bdev = I_BDEV(inode);
+	loff_t isize = i_size_read(inode);
+
+	iomap->bdev = bdev;
+	iomap->offset = ALIGN_DOWN(offset, bdev_logical_block_size(bdev));
+	if (WARN_ON_ONCE(iomap->offset >= isize))
+		return -EIO;
+	iomap->type = IOMAP_MAPPED;
+	iomap->addr = iomap->offset;
+	iomap->length = isize - iomap->offset;
+	iomap->flags |= IOMAP_F_BUFFER_HEAD;
+	return 0;
+}
+
+static const struct iomap_ops blkdev_iomap_ops = {
+	.iomap_begin		= blkdev_iomap_begin,
+};
+
 static int blkdev_writepage(struct page *page, struct writeback_control *wbc)
 {
 	return block_write_full_page(page, blkdev_get_block, wbc);
@@ -555,6 +577,11 @@ blkdev_direct_write(struct kiocb *iocb, struct iov_iter *from)
 	return written;
 }
 
+static ssize_t blkdev_buffered_write(struct kiocb *iocb, struct iov_iter *from)
+{
+	return iomap_file_buffered_write(iocb, from, &blkdev_iomap_ops);
+}
+
 /*
  * Write data to the block device.  Only intended for the block device itself
  * and the raw driver which basically is a fake block device.
@@ -604,9 +631,9 @@ static ssize_t blkdev_write_iter(struct kiocb *iocb, struct iov_iter *from)
 		ret = blkdev_direct_write(iocb, from);
 		if (ret >= 0 && iov_iter_count(from))
 			ret = direct_write_fallback(iocb, from, ret,
-					generic_perform_write(iocb, from));
+					blkdev_buffered_write(iocb, from));
 	} else {
-		ret = generic_perform_write(iocb, from);
+		ret = blkdev_buffered_write(iocb, from);
 	}
 
 	if (ret > 0)
-- 
2.39.2

Re: [PATCH 5/6] block: use iomap for writes to block devices

[Hannes Reinecke]

On 7/20/23 16:04, Christoph Hellwig wrote:
> Use iomap in buffer_head compat mode to write to block devices.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>   block/Kconfig |  1 +
>   block/fops.c  | 31 +++++++++++++++++++++++++++++--
>   2 files changed, 30 insertions(+), 2 deletions(-)
> 
Reviewed-by: Hannes Reinecke <hare@suse.de>

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                Kernel Storage Architect
hare@suse.de                              +49 911 74053 688
SUSE Software Solutions GmbH, Maxfeldstr. 5, 90409 Nürnberg
HRB 36809 (AG Nürnberg), Geschäftsführer: Ivo Totev, Andrew
Myers, Andrew McDonald, Martje Boudien Moerman

Re: [PATCH 5/6] block: use iomap for writes to block devices

[Luis Chamberlain]

On Thu, Jul 20, 2023 at 04:04:51PM +0200, Christoph Hellwig wrote:
> Use iomap in buffer_head compat mode to write to block devices.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>

Reviewed-by: Luis Chamberlain <mcgrof@kernel.org>

  Luis

Re: [PATCH 5/6] block: use iomap for writes to block devices

[Pankaj Raghav]

On Thu, Jul 20, 2023 at 04:04:51PM +0200, Christoph Hellwig wrote:
> Use iomap in buffer_head compat mode to write to block devices.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>

Looks good,
Reviewed-by: Pankaj Raghav <p.raghav@samsung.com>

[PATCH 6/6] fs: add CONFIG_BUFFER_HEAD

[Christoph Hellwig]

Add a new config option that controls building the buffer_head code, and
select it from all file systems and stacking drivers that need it.

For the block device nodes and alternative iomap based buffered I/O path
is provided when buffer_head support is not enabled, and iomap needs a
little tweak to be able to compile out the buffer_head based code path.

Otherwise this is just Kconfig and ifdef changes.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 block/fops.c                 | 71 +++++++++++++++++++++++++++++++-----
 drivers/md/Kconfig           |  1 +
 fs/Kconfig                   |  4 ++
 fs/Makefile                  |  2 +-
 fs/adfs/Kconfig              |  1 +
 fs/affs/Kconfig              |  1 +
 fs/befs/Kconfig              |  1 +
 fs/bfs/Kconfig               |  1 +
 fs/efs/Kconfig               |  1 +
 fs/exfat/Kconfig             |  1 +
 fs/ext2/Kconfig              |  1 +
 fs/ext4/Kconfig              |  1 +
 fs/f2fs/Kconfig              |  1 +
 fs/fat/Kconfig               |  1 +
 fs/freevxfs/Kconfig          |  1 +
 fs/gfs2/Kconfig              |  1 +
 fs/hfs/Kconfig               |  1 +
 fs/hfsplus/Kconfig           |  1 +
 fs/hpfs/Kconfig              |  1 +
 fs/iomap/buffered-io.c       | 12 ++++--
 fs/isofs/Kconfig             |  1 +
 fs/jfs/Kconfig               |  1 +
 fs/minix/Kconfig             |  1 +
 fs/nilfs2/Kconfig            |  1 +
 fs/ntfs/Kconfig              |  1 +
 fs/ntfs3/Kconfig             |  1 +
 fs/ocfs2/Kconfig             |  1 +
 fs/omfs/Kconfig              |  1 +
 fs/qnx4/Kconfig              |  1 +
 fs/qnx6/Kconfig              |  1 +
 fs/reiserfs/Kconfig          |  1 +
 fs/sysv/Kconfig              |  1 +
 fs/udf/Kconfig               |  1 +
 fs/ufs/Kconfig               |  1 +
 include/linux/buffer_head.h  | 32 ++++++++--------
 include/trace/events/block.h |  2 +
 mm/migrate.c                 |  4 +-
 37 files changed, 125 insertions(+), 32 deletions(-)

diff --git a/block/fops.c b/block/fops.c
index 31d356c83f27a3..57909430deb150 100644
--- a/block/fops.c
+++ b/block/fops.c
@@ -24,15 +24,6 @@ static inline struct inode *bdev_file_inode(struct file *file)
 	return file->f_mapping->host;
 }
 
-static int blkdev_get_block(struct inode *inode, sector_t iblock,
-		struct buffer_head *bh, int create)
-{
-	bh->b_bdev = I_BDEV(inode);
-	bh->b_blocknr = iblock;
-	set_buffer_mapped(bh);
-	return 0;
-}
-
 static blk_opf_t dio_bio_write_op(struct kiocb *iocb)
 {
 	blk_opf_t opf = REQ_OP_WRITE | REQ_SYNC | REQ_IDLE;
@@ -400,7 +391,8 @@ static int blkdev_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
 	iomap->type = IOMAP_MAPPED;
 	iomap->addr = iomap->offset;
 	iomap->length = isize - iomap->offset;
-	iomap->flags |= IOMAP_F_BUFFER_HEAD;
+	if (IS_ENABLED(CONFIG_BUFFER_HEAD))
+		iomap->flags |= IOMAP_F_BUFFER_HEAD;
 	return 0;
 }
 
@@ -408,6 +400,16 @@ static const struct iomap_ops blkdev_iomap_ops = {
 	.iomap_begin		= blkdev_iomap_begin,
 };
 
+#ifdef CONFIG_BUFFER_HEAD
+static int blkdev_get_block(struct inode *inode, sector_t iblock,
+		struct buffer_head *bh, int create)
+{
+	bh->b_bdev = I_BDEV(inode);
+	bh->b_blocknr = iblock;
+	set_buffer_mapped(bh);
+	return 0;
+}
+
 static int blkdev_writepage(struct page *page, struct writeback_control *wbc)
 {
 	return block_write_full_page(page, blkdev_get_block, wbc);
@@ -453,6 +455,55 @@ const struct address_space_operations def_blk_aops = {
 	.migrate_folio	= buffer_migrate_folio_norefs,
 	.is_dirty_writeback = buffer_check_dirty_writeback,
 };
+#else /* CONFIG_BUFFER_HEAD */
+static int blkdev_read_folio(struct file *file, struct folio *folio)
+{
+	return iomap_read_folio(folio, &blkdev_iomap_ops);
+}
+
+static void blkdev_readahead(struct readahead_control *rac)
+{
+	iomap_readahead(rac, &blkdev_iomap_ops);
+}
+
+static int blkdev_map_blocks(struct iomap_writepage_ctx *wpc,
+		struct inode *inode, loff_t offset)
+{
+	loff_t isize = i_size_read(inode);
+
+	if (WARN_ON_ONCE(offset >= isize))
+		return -EIO;
+	if (offset >= wpc->iomap.offset &&
+	    offset < wpc->iomap.offset + wpc->iomap.length)
+		return 0;
+	return blkdev_iomap_begin(inode, offset, isize - offset,
+				  IOMAP_WRITE, &wpc->iomap, NULL);
+}
+
+static const struct iomap_writeback_ops blkdev_writeback_ops = {
+	.map_blocks		= blkdev_map_blocks,
+};
+
+static int blkdev_writepages(struct address_space *mapping,
+		struct writeback_control *wbc)
+{
+	struct iomap_writepage_ctx wpc = { };
+
+	return iomap_writepages(mapping, wbc, &wpc, &blkdev_writeback_ops);
+}
+
+const struct address_space_operations def_blk_aops = {
+	.dirty_folio	= filemap_dirty_folio,
+	.release_folio		= iomap_release_folio,
+	.invalidate_folio	= iomap_invalidate_folio,
+	.read_folio		= blkdev_read_folio,
+	.readahead		= blkdev_readahead,
+	.writepages		= blkdev_writepages,
+	.is_partially_uptodate  = iomap_is_partially_uptodate,
+	.error_remove_page	= generic_error_remove_page,
+	.migrate_folio		= filemap_migrate_folio,
+};
+#endif /* CONFIG_BUFFER_HEAD */
 
 /*
  * for a block special file file_inode(file)->i_size is zero
diff --git a/drivers/md/Kconfig b/drivers/md/Kconfig
index b0a22e99bade37..9ee18013b1f2ab 100644
--- a/drivers/md/Kconfig
+++ b/drivers/md/Kconfig
@@ -15,6 +15,7 @@ if MD
 config BLK_DEV_MD
 	tristate "RAID support"
 	select BLOCK_HOLDER_DEPRECATED if SYSFS
+	select BUFFER_HEAD
 	# BLOCK_LEGACY_AUTOLOAD requirement should be removed
 	# after relevant mdadm enhancements - to make "names=yes"
 	# the default - are widely available.
diff --git a/fs/Kconfig b/fs/Kconfig
index 18d034ec79539f..e8b17c81b83a8e 100644
--- a/fs/Kconfig
+++ b/fs/Kconfig
@@ -18,8 +18,12 @@ config VALIDATE_FS_PARSER
 config FS_IOMAP
 	bool
 
+config BUFFER_HEAD
+	bool
+
 # old blockdev_direct_IO implementation.  Use iomap for new code instead
 config LEGACY_DIRECT_IO
+	depends on BUFFER_HEAD
 	bool
 
 if BLOCK
diff --git a/fs/Makefile b/fs/Makefile
index e513aaee0603a0..f9541f40be4e08 100644
--- a/fs/Makefile
+++ b/fs/Makefile
@@ -17,7 +17,7 @@ obj-y :=	open.o read_write.o file_table.o super.o \
 		fs_types.o fs_context.o fs_parser.o fsopen.o init.o \
 		kernel_read_file.o mnt_idmapping.o remap_range.o
 
-obj-$(CONFIG_BLOCK)		+= buffer.o mpage.o
+obj-$(CONFIG_BUFFER_HEAD)	+= buffer.o mpage.o
 obj-$(CONFIG_PROC_FS)		+= proc_namespace.o
 obj-$(CONFIG_LEGACY_DIRECT_IO)	+= direct-io.o
 obj-y				+= notify/
diff --git a/fs/adfs/Kconfig b/fs/adfs/Kconfig
index 44738fed66251f..1b97058f0c4a92 100644
--- a/fs/adfs/Kconfig
+++ b/fs/adfs/Kconfig
@@ -2,6 +2,7 @@
 config ADFS_FS
 	tristate "ADFS file system support"
 	depends on BLOCK
+	select BUFFER_HEAD
 	help
 	  The Acorn Disc Filing System is the standard file system of the
 	  RiscOS operating system which runs on Acorn's ARM-based Risc PC
diff --git a/fs/affs/Kconfig b/fs/affs/Kconfig
index 962b86374e1c15..1ae432d266c32f 100644
--- a/fs/affs/Kconfig
+++ b/fs/affs/Kconfig
@@ -2,6 +2,7 @@
 config AFFS_FS
 	tristate "Amiga FFS file system support"
 	depends on BLOCK
+	select BUFFER_HEAD
 	select LEGACY_DIRECT_IO
 	help
 	  The Fast File System (FFS) is the common file system used on hard
diff --git a/fs/befs/Kconfig b/fs/befs/Kconfig
index 9550b6462b8147..5fcfc4024ffe6f 100644
--- a/fs/befs/Kconfig
+++ b/fs/befs/Kconfig
@@ -2,6 +2,7 @@
 config BEFS_FS
 	tristate "BeOS file system (BeFS) support (read only)"
 	depends on BLOCK
+	select BUFFER_HEAD
 	select NLS
 	help
 	  The BeOS File System (BeFS) is the native file system of Be, Inc's
diff --git a/fs/bfs/Kconfig b/fs/bfs/Kconfig
index 3a757805b58568..8e7ef866b62a62 100644
--- a/fs/bfs/Kconfig
+++ b/fs/bfs/Kconfig
@@ -2,6 +2,7 @@
 config BFS_FS
 	tristate "BFS file system support"
 	depends on BLOCK
+	select BUFFER_HEAD
 	help
 	  Boot File System (BFS) is a file system used under SCO UnixWare to
 	  allow the bootloader access to the kernel image and other important
diff --git a/fs/efs/Kconfig b/fs/efs/Kconfig
index 2df1bac8b375b1..0833e533df9d53 100644
--- a/fs/efs/Kconfig
+++ b/fs/efs/Kconfig
@@ -2,6 +2,7 @@
 config EFS_FS
 	tristate "EFS file system support (read only)"
 	depends on BLOCK
+	select BUFFER_HEAD
 	help
 	  EFS is an older file system used for non-ISO9660 CD-ROMs and hard
 	  disk partitions by SGI's IRIX operating system (IRIX 6.0 and newer
diff --git a/fs/exfat/Kconfig b/fs/exfat/Kconfig
index 147edeb044691d..cbeca8e44d9b38 100644
--- a/fs/exfat/Kconfig
+++ b/fs/exfat/Kconfig
@@ -2,6 +2,7 @@
 
 config EXFAT_FS
 	tristate "exFAT filesystem support"
+	select BUFFER_HEAD
 	select NLS
 	select LEGACY_DIRECT_IO
 	help
diff --git a/fs/ext2/Kconfig b/fs/ext2/Kconfig
index 77393fda99af09..74d98965902e16 100644
--- a/fs/ext2/Kconfig
+++ b/fs/ext2/Kconfig
@@ -1,6 +1,7 @@
 # SPDX-License-Identifier: GPL-2.0-only
 config EXT2_FS
 	tristate "Second extended fs support"
+	select BUFFER_HEAD
 	select FS_IOMAP
 	select LEGACY_DIRECT_IO
 	help
diff --git a/fs/ext4/Kconfig b/fs/ext4/Kconfig
index 86699c8cab281c..e20d59221fc05b 100644
--- a/fs/ext4/Kconfig
+++ b/fs/ext4/Kconfig
@@ -28,6 +28,7 @@ config EXT3_FS_SECURITY
 
 config EXT4_FS
 	tristate "The Extended 4 (ext4) filesystem"
+	select BUFFER_HEAD
 	select JBD2
 	select CRC16
 	select CRYPTO
diff --git a/fs/f2fs/Kconfig b/fs/f2fs/Kconfig
index 03ef087537c7c4..68a1e23e1557c7 100644
--- a/fs/f2fs/Kconfig
+++ b/fs/f2fs/Kconfig
@@ -2,6 +2,7 @@
 config F2FS_FS
 	tristate "F2FS filesystem support"
 	depends on BLOCK
+	select BUFFER_HEAD
 	select NLS
 	select CRYPTO
 	select CRYPTO_CRC32
diff --git a/fs/fat/Kconfig b/fs/fat/Kconfig
index afe83b4e717280..25fae1c83725bc 100644
--- a/fs/fat/Kconfig
+++ b/fs/fat/Kconfig
@@ -1,6 +1,7 @@
 # SPDX-License-Identifier: GPL-2.0-only
 config FAT_FS
 	tristate
+	select BUFFER_HEAD
 	select NLS
 	select LEGACY_DIRECT_IO
 	help
diff --git a/fs/freevxfs/Kconfig b/fs/freevxfs/Kconfig
index 0e2fc08f7de492..912107ebea6f40 100644
--- a/fs/freevxfs/Kconfig
+++ b/fs/freevxfs/Kconfig
@@ -2,6 +2,7 @@
 config VXFS_FS
 	tristate "FreeVxFS file system support (VERITAS VxFS(TM) compatible)"
 	depends on BLOCK
+	select BUFFER_HEAD
 	help
 	  FreeVxFS is a file system driver that support the VERITAS VxFS(TM)
 	  file system format.  VERITAS VxFS(TM) is the standard file system
diff --git a/fs/gfs2/Kconfig b/fs/gfs2/Kconfig
index 03c966840422ec..be7f87a8e11ae1 100644
--- a/fs/gfs2/Kconfig
+++ b/fs/gfs2/Kconfig
@@ -1,6 +1,7 @@
 # SPDX-License-Identifier: GPL-2.0-only
 config GFS2_FS
 	tristate "GFS2 file system support"
+	select BUFFER_HEAD
 	select FS_POSIX_ACL
 	select CRC32
 	select LIBCRC32C
diff --git a/fs/hfs/Kconfig b/fs/hfs/Kconfig
index d985066006d588..5ea5cd8ecea9c0 100644
--- a/fs/hfs/Kconfig
+++ b/fs/hfs/Kconfig
@@ -2,6 +2,7 @@
 config HFS_FS
 	tristate "Apple Macintosh file system support"
 	depends on BLOCK
+	select BUFFER_HEAD
 	select NLS
 	select LEGACY_DIRECT_IO
 	help
diff --git a/fs/hfsplus/Kconfig b/fs/hfsplus/Kconfig
index 8034e7827a690b..8ce4a33a9ac788 100644
--- a/fs/hfsplus/Kconfig
+++ b/fs/hfsplus/Kconfig
@@ -2,6 +2,7 @@
 config HFSPLUS_FS
 	tristate "Apple Extended HFS file system support"
 	depends on BLOCK
+	select BUFFER_HEAD
 	select NLS
 	select NLS_UTF8
 	select LEGACY_DIRECT_IO
diff --git a/fs/hpfs/Kconfig b/fs/hpfs/Kconfig
index ec975f4668775f..ac1e9318e65a4a 100644
--- a/fs/hpfs/Kconfig
+++ b/fs/hpfs/Kconfig
@@ -2,6 +2,7 @@
 config HPFS_FS
 	tristate "OS/2 HPFS file system support"
 	depends on BLOCK
+	select BUFFER_HEAD
 	select FS_IOMAP
 	help
 	  OS/2 is IBM's operating system for PC's, the same as Warp, and HPFS
diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index 0607790827b48a..6dc585c010c020 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -41,6 +41,12 @@ static inline struct iomap_page *to_iomap_page(struct folio *folio)
 	return NULL;
 }
 
+static inline bool iomap_use_buffer_heads(const struct iomap *iomap)
+{
+	return IS_ENABLED(CONFIG_BUFFER_HEAD) &&
+		(iomap->flags & IOMAP_F_BUFFER_HEAD);
+}
+
 static struct bio_set iomap_ioend_bioset;
 
 static struct iomap_page *
@@ -675,7 +681,7 @@ static int iomap_write_begin(struct iomap_iter *iter, loff_t pos,
 
 	if (srcmap->type == IOMAP_INLINE)
 		status = iomap_write_begin_inline(iter, folio);
-	else if (srcmap->flags & IOMAP_F_BUFFER_HEAD)
+	else if (iomap_use_buffer_heads(srcmap))
 		status = __block_write_begin_int(folio, pos, len, NULL, srcmap);
 	else
 		status = __iomap_write_begin(iter, pos, len, folio);
@@ -745,7 +751,7 @@ static size_t iomap_write_end(struct iomap_iter *iter, loff_t pos, size_t len,
 
 	if (srcmap->type == IOMAP_INLINE) {
 		ret = iomap_write_end_inline(iter, folio, pos, copied);
-	} else if (srcmap->flags & IOMAP_F_BUFFER_HEAD) {
+	} else if (iomap_use_buffer_heads(srcmap)) {
 		ret = block_write_end(NULL, iter->inode->i_mapping, pos, len,
 				copied, &folio->page, NULL);
 	} else {
@@ -1248,7 +1254,7 @@ static loff_t iomap_folio_mkwrite_iter(struct iomap_iter *iter,
 	loff_t length = iomap_length(iter);
 	int ret;
 
-	if (iter->iomap.flags & IOMAP_F_BUFFER_HEAD) {
+	if (iomap_use_buffer_heads(&iter->iomap)) {
 		ret = __block_write_begin_int(folio, iter->pos, length, NULL,
 					      &iter->iomap);
 		if (ret)
diff --git a/fs/isofs/Kconfig b/fs/isofs/Kconfig
index 08ffd37b9bb8f6..51434f2a471b0f 100644
--- a/fs/isofs/Kconfig
+++ b/fs/isofs/Kconfig
@@ -1,6 +1,7 @@
 # SPDX-License-Identifier: GPL-2.0-only
 config ISO9660_FS
 	tristate "ISO 9660 CDROM file system support"
+	select BUFFER_HEAD
 	help
 	  This is the standard file system used on CD-ROMs.  It was previously
 	  known as "High Sierra File System" and is called "hsfs" on other
diff --git a/fs/jfs/Kconfig b/fs/jfs/Kconfig
index 51e856f0e4b8d6..17488440eef1a9 100644
--- a/fs/jfs/Kconfig
+++ b/fs/jfs/Kconfig
@@ -1,6 +1,7 @@
 # SPDX-License-Identifier: GPL-2.0-only
 config JFS_FS
 	tristate "JFS filesystem support"
+	select BUFFER_HEAD
 	select NLS
 	select CRC32
 	select LEGACY_DIRECT_IO
diff --git a/fs/minix/Kconfig b/fs/minix/Kconfig
index de2003974ff0d0..90ddfad2a75e8f 100644
--- a/fs/minix/Kconfig
+++ b/fs/minix/Kconfig
@@ -2,6 +2,7 @@
 config MINIX_FS
 	tristate "Minix file system support"
 	depends on BLOCK
+	select BUFFER_HEAD
 	help
 	  Minix is a simple operating system used in many classes about OS's.
 	  The minix file system (method to organize files on a hard disk
diff --git a/fs/nilfs2/Kconfig b/fs/nilfs2/Kconfig
index 7d59567465e121..7dae168e346e30 100644
--- a/fs/nilfs2/Kconfig
+++ b/fs/nilfs2/Kconfig
@@ -1,6 +1,7 @@
 # SPDX-License-Identifier: GPL-2.0-only
 config NILFS2_FS
 	tristate "NILFS2 file system support"
+	select BUFFER_HEAD
 	select CRC32
 	select LEGACY_DIRECT_IO
 	help
diff --git a/fs/ntfs/Kconfig b/fs/ntfs/Kconfig
index f93e69a612833f..7b2509741735a9 100644
--- a/fs/ntfs/Kconfig
+++ b/fs/ntfs/Kconfig
@@ -1,6 +1,7 @@
 # SPDX-License-Identifier: GPL-2.0-only
 config NTFS_FS
 	tristate "NTFS file system support"
+	select BUFFER_HEAD
 	select NLS
 	help
 	  NTFS is the file system of Microsoft Windows NT, 2000, XP and 2003.
diff --git a/fs/ntfs3/Kconfig b/fs/ntfs3/Kconfig
index 96cc236f7f7bd3..cdfdf51e55d797 100644
--- a/fs/ntfs3/Kconfig
+++ b/fs/ntfs3/Kconfig
@@ -1,6 +1,7 @@
 # SPDX-License-Identifier: GPL-2.0-only
 config NTFS3_FS
 	tristate "NTFS Read-Write file system support"
+	select BUFFER_HEAD
 	select NLS
 	select LEGACY_DIRECT_IO
 	help
diff --git a/fs/ocfs2/Kconfig b/fs/ocfs2/Kconfig
index 3123da7cfb301f..2514d36cbe0157 100644
--- a/fs/ocfs2/Kconfig
+++ b/fs/ocfs2/Kconfig
@@ -2,6 +2,7 @@
 config OCFS2_FS
 	tristate "OCFS2 file system support"
 	depends on INET && SYSFS && CONFIGFS_FS
+	select BUFFER_HEAD
 	select JBD2
 	select CRC32
 	select QUOTA
diff --git a/fs/omfs/Kconfig b/fs/omfs/Kconfig
index 42b2ec35a05bfb..8470f6c3e64e6a 100644
--- a/fs/omfs/Kconfig
+++ b/fs/omfs/Kconfig
@@ -2,6 +2,7 @@
 config OMFS_FS
 	tristate "SonicBlue Optimized MPEG File System support"
 	depends on BLOCK
+	select BUFFER_HEAD
 	select CRC_ITU_T
 	help
 	  This is the proprietary file system used by the Rio Karma music
diff --git a/fs/qnx4/Kconfig b/fs/qnx4/Kconfig
index 45b5b98376c436..a2eb826e76c602 100644
--- a/fs/qnx4/Kconfig
+++ b/fs/qnx4/Kconfig
@@ -2,6 +2,7 @@
 config QNX4FS_FS
 	tristate "QNX4 file system support (read only)"
 	depends on BLOCK
+	select BUFFER_HEAD
 	help
 	  This is the file system used by the real-time operating systems
 	  QNX 4 and QNX 6 (the latter is also called QNX RTP).
diff --git a/fs/qnx6/Kconfig b/fs/qnx6/Kconfig
index 6a9d6bce158622..8e865d72204e75 100644
--- a/fs/qnx6/Kconfig
+++ b/fs/qnx6/Kconfig
@@ -2,6 +2,7 @@
 config QNX6FS_FS
 	tristate "QNX6 file system support (read only)"
 	depends on BLOCK && CRC32
+	select BUFFER_HEAD
 	help
 	  This is the file system used by the real-time operating systems
 	  QNX 6 (also called QNX RTP).
diff --git a/fs/reiserfs/Kconfig b/fs/reiserfs/Kconfig
index 4d22ecfe0fab65..0e6fe26458fede 100644
--- a/fs/reiserfs/Kconfig
+++ b/fs/reiserfs/Kconfig
@@ -1,6 +1,7 @@
 # SPDX-License-Identifier: GPL-2.0-only
 config REISERFS_FS
 	tristate "Reiserfs support (deprecated)"
+	select BUFFER_HEAD
 	select CRC32
 	select LEGACY_DIRECT_IO
 	help
diff --git a/fs/sysv/Kconfig b/fs/sysv/Kconfig
index b4e23e03fbeba3..67b3f90afbfd67 100644
--- a/fs/sysv/Kconfig
+++ b/fs/sysv/Kconfig
@@ -2,6 +2,7 @@
 config SYSV_FS
 	tristate "System V/Xenix/V7/Coherent file system support"
 	depends on BLOCK
+	select BUFFER_HEAD
 	help
 	  SCO, Xenix and Coherent are commercial Unix systems for Intel
 	  machines, and Version 7 was used on the DEC PDP-11. Saying Y
diff --git a/fs/udf/Kconfig b/fs/udf/Kconfig
index 82e8bfa2dfd989..8f7ce30d47fdce 100644
--- a/fs/udf/Kconfig
+++ b/fs/udf/Kconfig
@@ -1,6 +1,7 @@
 # SPDX-License-Identifier: GPL-2.0-only
 config UDF_FS
 	tristate "UDF file system support"
+	select BUFFER_HEAD
 	select CRC_ITU_T
 	select NLS
 	select LEGACY_DIRECT_IO
diff --git a/fs/ufs/Kconfig b/fs/ufs/Kconfig
index 6d30adb6b890fc..9301e7ecd09210 100644
--- a/fs/ufs/Kconfig
+++ b/fs/ufs/Kconfig
@@ -2,6 +2,7 @@
 config UFS_FS
 	tristate "UFS file system support (read only)"
 	depends on BLOCK
+	select BUFFER_HEAD
 	help
 	  BSD and derivate versions of Unix (such as SunOS, FreeBSD, NetBSD,
 	  OpenBSD and NeXTstep) use a file system called UFS. Some System V
diff --git a/include/linux/buffer_head.h b/include/linux/buffer_head.h
index 7002a9ff63a3da..c89ef50d5112fc 100644
--- a/include/linux/buffer_head.h
+++ b/include/linux/buffer_head.h
@@ -16,8 +16,6 @@
 #include <linux/wait.h>
 #include <linux/atomic.h>
 
-#ifdef CONFIG_BLOCK
-
 enum bh_state_bits {
 	BH_Uptodate,	/* Contains valid data */
 	BH_Dirty,	/* Is dirty */
@@ -198,7 +196,6 @@ void set_bh_page(struct buffer_head *bh,
 		struct page *page, unsigned long offset);
 void folio_set_bh(struct buffer_head *bh, struct folio *folio,
 		  unsigned long offset);
-bool try_to_free_buffers(struct folio *);
 struct buffer_head *folio_alloc_buffers(struct folio *folio, unsigned long size,
 					bool retry);
 struct buffer_head *alloc_page_buffers(struct page *page, unsigned long size,
@@ -213,10 +210,6 @@ void end_buffer_async_write(struct buffer_head *bh, int uptodate);
 
 /* Things to do with buffers at mapping->private_list */
 void mark_buffer_dirty_inode(struct buffer_head *bh, struct inode *inode);
-int inode_has_buffers(struct inode *);
-void invalidate_inode_buffers(struct inode *);
-int remove_inode_buffers(struct inode *inode);
-int sync_mapping_buffers(struct address_space *mapping);
 int generic_buffers_fsync_noflush(struct file *file, loff_t start, loff_t end,
 				  bool datasync);
 int generic_buffers_fsync(struct file *file, loff_t start, loff_t end,
@@ -240,9 +233,6 @@ void __bforget(struct buffer_head *);
 void __breadahead(struct block_device *, sector_t block, unsigned int size);
 struct buffer_head *__bread_gfp(struct block_device *,
 				sector_t block, unsigned size, gfp_t gfp);
-void invalidate_bh_lrus(void);
-void invalidate_bh_lrus_cpu(void);
-bool has_bh_in_lru(int cpu, void *dummy);
 struct buffer_head *alloc_buffer_head(gfp_t gfp_flags);
 void free_buffer_head(struct buffer_head * bh);
 void unlock_buffer(struct buffer_head *bh);
@@ -258,8 +248,6 @@ int __bh_read(struct buffer_head *bh, blk_opf_t op_flags, bool wait);
 void __bh_read_batch(int nr, struct buffer_head *bhs[],
 		     blk_opf_t op_flags, bool force_lock);
 
-extern int buffer_heads_over_limit;
-
 /*
  * Generic address_space_operations implementations for buffer_head-backed
  * address_spaces.
@@ -304,8 +292,6 @@ extern int buffer_migrate_folio_norefs(struct address_space *,
 #define buffer_migrate_folio_norefs NULL
 #endif
 
-void buffer_init(void);
-
 /*
  * inline definitions
  */
@@ -465,7 +451,20 @@ __bread(struct block_device *bdev, sector_t block, unsigned size)
 
 bool block_dirty_folio(struct address_space *mapping, struct folio *folio);
 
-#else /* CONFIG_BLOCK */
+#ifdef CONFIG_BUFFER_HEAD
+
+void buffer_init(void);
+bool try_to_free_buffers(struct folio *folio);
+int inode_has_buffers(struct inode *inode);
+void invalidate_inode_buffers(struct inode *inode);
+int remove_inode_buffers(struct inode *inode);
+int sync_mapping_buffers(struct address_space *mapping);
+void invalidate_bh_lrus(void);
+void invalidate_bh_lrus_cpu(void);
+bool has_bh_in_lru(int cpu, void *dummy);
+extern int buffer_heads_over_limit;
+
+#else /* CONFIG_BUFFER_HEAD */
 
 static inline void buffer_init(void) {}
 static inline bool try_to_free_buffers(struct folio *folio) { return true; }
@@ -473,9 +472,10 @@ static inline int inode_has_buffers(struct inode *inode) { return 0; }
 static inline void invalidate_inode_buffers(struct inode *inode) {}
 static inline int remove_inode_buffers(struct inode *inode) { return 1; }
 static inline int sync_mapping_buffers(struct address_space *mapping) { return 0; }
+static inline void invalidate_bh_lrus(void) {}
 static inline void invalidate_bh_lrus_cpu(void) {}
 static inline bool has_bh_in_lru(int cpu, void *dummy) { return false; }
 #define buffer_heads_over_limit 0
 
-#endif /* CONFIG_BLOCK */
+#endif /* CONFIG_BUFFER_HEAD */
 #endif /* _LINUX_BUFFER_HEAD_H */
diff --git a/include/trace/events/block.h b/include/trace/events/block.h
index 40e60c33cc6f3d..0e128ad5146015 100644
--- a/include/trace/events/block.h
+++ b/include/trace/events/block.h
@@ -12,6 +12,7 @@
 
 #define RWBS_LEN	8
 
+#ifdef CONFIG_BUFFER_HEAD
 DECLARE_EVENT_CLASS(block_buffer,
 
 	TP_PROTO(struct buffer_head *bh),
@@ -61,6 +62,7 @@ DEFINE_EVENT(block_buffer, block_dirty_buffer,
 
 	TP_ARGS(bh)
 );
+#endif /* CONFIG_BUFFER_HEAD */
 
 /**
  * block_rq_requeue - place block IO request back on a queue
diff --git a/mm/migrate.c b/mm/migrate.c
index 24baad2571e314..fe6f8d454aff83 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -684,7 +684,7 @@ int migrate_folio(struct address_space *mapping, struct folio *dst,
 }
 EXPORT_SYMBOL(migrate_folio);
 
-#ifdef CONFIG_BLOCK
+#ifdef CONFIG_BUFFER_HEAD
 /* Returns true if all buffers are successfully locked */
 static bool buffer_migrate_lock_buffers(struct buffer_head *head,
 							enum migrate_mode mode)
@@ -837,7 +837,7 @@ int buffer_migrate_folio_norefs(struct address_space *mapping,
 	return __buffer_migrate_folio(mapping, dst, src, mode, true);
 }
 EXPORT_SYMBOL_GPL(buffer_migrate_folio_norefs);
-#endif
+#endif /* CONFIG_BUFFER_HEAD */
 
 int filemap_migrate_folio(struct address_space *mapping,
 		struct folio *dst, struct folio *src, enum migrate_mode mode)
-- 
2.39.2

Re: [PATCH 6/6] fs: add CONFIG_BUFFER_HEAD

[Matthew Wilcox]

On Thu, Jul 20, 2023 at 04:04:52PM +0200, Christoph Hellwig wrote:
> @@ -400,7 +391,8 @@ static int blkdev_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
>  	iomap->type = IOMAP_MAPPED;
>  	iomap->addr = iomap->offset;
>  	iomap->length = isize - iomap->offset;
> -	iomap->flags |= IOMAP_F_BUFFER_HEAD;
> +	if (IS_ENABLED(CONFIG_BUFFER_HEAD))
> +		iomap->flags |= IOMAP_F_BUFFER_HEAD;

Wouldn't it be simpler to do ...

+#ifdef CONFIG_BUFFER_HEAD
 #define IOMAP_F_BUFFER_HEAD     (1U << 4)
+#else
+#define IOMAP_F_BUFFER_HEAD	0
+#endif

in include/linux/iomap.h ?

> diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
> index 0607790827b48a..6dc585c010c020 100644
> --- a/fs/iomap/buffered-io.c
> +++ b/fs/iomap/buffered-io.c
> @@ -41,6 +41,12 @@ static inline struct iomap_page *to_iomap_page(struct folio *folio)
>  	return NULL;
>  }
>  
> +static inline bool iomap_use_buffer_heads(const struct iomap *iomap)
> +{
> +	return IS_ENABLED(CONFIG_BUFFER_HEAD) &&
> +		(iomap->flags & IOMAP_F_BUFFER_HEAD);
> +}

... because this function then goes away.

> @@ -675,7 +681,7 @@ static int iomap_write_begin(struct iomap_iter *iter, loff_t pos,
>  
>  	if (srcmap->type == IOMAP_INLINE)
>  		status = iomap_write_begin_inline(iter, folio);
> -	else if (srcmap->flags & IOMAP_F_BUFFER_HEAD)
> +	else if (iomap_use_buffer_heads(srcmap))

... as this will be optimised away.

Re: [PATCH 6/6] fs: add CONFIG_BUFFER_HEAD

[Christoph Hellwig]

On Thu, Jul 20, 2023 at 03:45:11PM +0100, Matthew Wilcox wrote:
> On Thu, Jul 20, 2023 at 04:04:52PM +0200, Christoph Hellwig wrote:
> > @@ -400,7 +391,8 @@ static int blkdev_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
> >  	iomap->type = IOMAP_MAPPED;
> >  	iomap->addr = iomap->offset;
> >  	iomap->length = isize - iomap->offset;
> > -	iomap->flags |= IOMAP_F_BUFFER_HEAD;
> > +	if (IS_ENABLED(CONFIG_BUFFER_HEAD))
> > +		iomap->flags |= IOMAP_F_BUFFER_HEAD;
> 
> Wouldn't it be simpler to do ...
> 
> +#ifdef CONFIG_BUFFER_HEAD
>  #define IOMAP_F_BUFFER_HEAD     (1U << 4)
> +#else
> +#define IOMAP_F_BUFFER_HEAD	0
> +#endif
> 
> in include/linux/iomap.h ?

> ... because this function then goes away.

I guess we could do that.  It is less intrusive, but I have to say I find
flags that get defined away to 0 fairly confusing for the reader.

Re: [PATCH 6/6] fs: add CONFIG_BUFFER_HEAD

[Hannes Reinecke]

On 7/20/23 16:04, Christoph Hellwig wrote:
> Add a new config option that controls building the buffer_head code, and
> select it from all file systems and stacking drivers that need it.
> 
> For the block device nodes and alternative iomap based buffered I/O path
> is provided when buffer_head support is not enabled, and iomap needs a
> little tweak to be able to compile out the buffer_head based code path.
> 
> Otherwise this is just Kconfig and ifdef changes.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>   block/fops.c                 | 71 +++++++++++++++++++++++++++++++-----
>   drivers/md/Kconfig           |  1 +
>   fs/Kconfig                   |  4 ++
>   fs/Makefile                  |  2 +-
>   fs/adfs/Kconfig              |  1 +
>   fs/affs/Kconfig              |  1 +
>   fs/befs/Kconfig              |  1 +
>   fs/bfs/Kconfig               |  1 +
>   fs/efs/Kconfig               |  1 +
>   fs/exfat/Kconfig             |  1 +
>   fs/ext2/Kconfig              |  1 +
>   fs/ext4/Kconfig              |  1 +
>   fs/f2fs/Kconfig              |  1 +
>   fs/fat/Kconfig               |  1 +
>   fs/freevxfs/Kconfig          |  1 +
>   fs/gfs2/Kconfig              |  1 +
>   fs/hfs/Kconfig               |  1 +
>   fs/hfsplus/Kconfig           |  1 +
>   fs/hpfs/Kconfig              |  1 +
>   fs/iomap/buffered-io.c       | 12 ++++--
>   fs/isofs/Kconfig             |  1 +
>   fs/jfs/Kconfig               |  1 +
>   fs/minix/Kconfig             |  1 +
>   fs/nilfs2/Kconfig            |  1 +
>   fs/ntfs/Kconfig              |  1 +
>   fs/ntfs3/Kconfig             |  1 +
>   fs/ocfs2/Kconfig             |  1 +
>   fs/omfs/Kconfig              |  1 +
>   fs/qnx4/Kconfig              |  1 +
>   fs/qnx6/Kconfig              |  1 +
>   fs/reiserfs/Kconfig          |  1 +
>   fs/sysv/Kconfig              |  1 +
>   fs/udf/Kconfig               |  1 +
>   fs/ufs/Kconfig               |  1 +
>   include/linux/buffer_head.h  | 32 ++++++++--------
>   include/trace/events/block.h |  2 +
>   mm/migrate.c                 |  4 +-
>   37 files changed, 125 insertions(+), 32 deletions(-)
> 
Hmm.

I actually have a patchset which _does_ allow for large I/O blocksizes 
with buffer_heads. (And even ltp/fsx is happy on xfs...)

Can we modify this to not have a compile-time option but rather a 
setting somewhere? EG kernel option or flag in struct address_space?

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                Kernel Storage Architect
hare@suse.de                              +49 911 74053 688
SUSE Software Solutions GmbH, Maxfeldstr. 5, 90409 Nürnberg
HRB 36809 (AG Nürnberg), Geschäftsführer: Ivo Totev, Andrew
Myers, Andrew McDonald, Martje Boudien Moerman

Re: [PATCH 6/6] fs: add CONFIG_BUFFER_HEAD

[Christoph Hellwig]

On Thu, Jul 20, 2023 at 05:53:52PM +0200, Hannes Reinecke wrote:
> Can we modify this to not have a compile-time option but rather a setting 
> somewhere? EG kernel option or flag in struct address_space?

Modify what?  The current code diables buffer_head suport on the
block devices when the kernel does not support buffer_heads.  There
is no good way to make that a run time decision :)

Re: [PATCH 6/6] fs: add CONFIG_BUFFER_HEAD

[Luis Chamberlain]

On Thu, Jul 20, 2023 at 04:04:52PM +0200, Christoph Hellwig wrote:
> Add a new config option that controls building the buffer_head code, and
> select it from all file systems and stacking drivers that need it.
> 
> For the block device nodes and alternative iomap based buffered I/O path
> is provided when buffer_head support is not enabled, and iomap needs a
> little tweak to be able to compile out the buffer_head based code path.
> 
> Otherwise this is just Kconfig and ifdef changes.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>

Reviewed-by: Luis Chamberlain <mcgrof@kernel.org>

  Luis

Re: allow building a kernel without buffer_heads

[Bob Peterson]

On 7/20/23 9:04 AM, Christoph Hellwig wrote:
> Hi all,
> 
> This series allows to build a kernel without buffer_heads, which I
> think is useful to show where the dependencies are, and maybe also
> for some very much limited environments, where people just needs
> xfs and/or btrfs and some of the read-only block based file systems.
> 
> It first switches buffered writes (but not writeback) for block devices
> to use iomap unconditionally, but still using buffer_heads, and then
> adds a CONFIG_BUFFER_HEAD selected by all file systems that need it
> (which is most block based file systems), makes the buffer_head support
> in iomap optional, and adds an alternative implementation of the block
> device address_operations using iomap.  This latter implementation
> will also be useful to support block size > PAGE_SIZE for block device
> nodes as buffer_heads won't work very well for that.
> 
> Note that for now the md software raid drivers is also disabled as it has
> some (rather questionable) buffer_head usage in the unconditionally built
> bitmap code.  I have a series pending to make the bitmap code conditional
> and deprecated it, but it hasn't been merged yet.
> 
> Changes since v1:
>   - drop the already merged prep patches
>   - depend on FS_IOMAP not IOMAP
>   - pick a better new name for block_page_mkwrite_return
> 
Hi Christoph,

Gfs2 still uses buffer_heads to manage the metadata being pushed through 
its journals. We've been reducing our dependency on them but eliminating 
them altogether is a large and daunting task. We can still work toward 
that goal, but it will take time.

Bob Peterson

Re: allow building a kernel without buffer_heads

[Christoph Hellwig]

On Thu, Jul 20, 2023 at 09:51:30AM -0500, Bob Peterson wrote:
> Gfs2 still uses buffer_heads to manage the metadata being pushed through 
> its journals. We've been reducing our dependency on them but eliminating 
> them altogether is a large and daunting task. We can still work toward that 
> goal, but it will take time.

That's fine - gfs2 selects CONFIG_BUFFER_HEAD after this series and
will be perfectly fine.