[PATCH RFC] block: enable RWF_DONTCACHE for block devices

[PATCH RFC] block: enable RWF_DONTCACHE for block devices

[Tal Zussman]

Block device buffered reads and writes already pass through
filemap_read() and iomap_file_buffered_write() respectively, both of
which handle IOCB_DONTCACHE. Enable RWF_DONTCACHE for block device files
by setting FOP_DONTCACHE in def_blk_fops.

For CONFIG_BUFFER_HEAD paths, thread the kiocb through
block_write_begin() so that buffer_head-based I/O can use DONTCACHE
behavior as well. Callers without a kiocb context (e.g. nilfs2 recovery)
pass NULL, which preserves the existing behavior.

This support is useful for databases that operate on raw block devices,
among other userspace applications.

Signed-off-by: Tal Zussman <tz2294@columbia.edu>
---
This is based on v6.19. Please let me know if there's a different tree I
should base this on.

I wasn't sure if the block_write_begin() changes were necessary for
block device support if CONFIG_BUFFER_HEAD is set (hence the RFC tag). I
can remove those if they're not necessary.
---
 block/fops.c                |  4 ++--
 fs/bfs/file.c               |  2 +-
 fs/buffer.c                 | 12 ++++++++----
 fs/exfat/inode.c            |  2 +-
 fs/ext2/inode.c             |  2 +-
 fs/jfs/inode.c              |  2 +-
 fs/minix/inode.c            |  2 +-
 fs/nilfs2/inode.c           |  2 +-
 fs/nilfs2/recovery.c        |  2 +-
 fs/ntfs3/inode.c            |  2 +-
 fs/omfs/file.c              |  2 +-
 fs/udf/inode.c              |  2 +-
 fs/ufs/inode.c              |  2 +-
 include/linux/buffer_head.h |  5 +++--
 14 files changed, 24 insertions(+), 19 deletions(-)

diff --git a/block/fops.c b/block/fops.c
index 4d32785b31d9..6bc727f8b252 100644
--- a/block/fops.c
+++ b/block/fops.c
@@ -505,7 +505,7 @@ static int blkdev_write_begin(const struct kiocb *iocb,
 			      unsigned len, struct folio **foliop,
 			      void **fsdata)
 {
-	return block_write_begin(mapping, pos, len, foliop, blkdev_get_block);
+	return block_write_begin(iocb, mapping, pos, len, foliop, blkdev_get_block);
 }
 
 static int blkdev_write_end(const struct kiocb *iocb,
@@ -967,7 +967,7 @@ const struct file_operations def_blk_fops = {
 	.splice_write	= iter_file_splice_write,
 	.fallocate	= blkdev_fallocate,
 	.uring_cmd	= blkdev_uring_cmd,
-	.fop_flags	= FOP_BUFFER_RASYNC,
+	.fop_flags	= FOP_BUFFER_RASYNC | FOP_DONTCACHE,
 };
 
 static __init int blkdev_init(void)
diff --git a/fs/bfs/file.c b/fs/bfs/file.c
index d33d6bde992b..f2804e38b8a7 100644
--- a/fs/bfs/file.c
+++ b/fs/bfs/file.c
@@ -177,7 +177,7 @@ static int bfs_write_begin(const struct kiocb *iocb,
 {
 	int ret;
 
-	ret = block_write_begin(mapping, pos, len, foliop, bfs_get_block);
+	ret = block_write_begin(iocb, mapping, pos, len, foliop, bfs_get_block);
 	if (unlikely(ret))
 		bfs_write_failed(mapping, pos + len);
 
diff --git a/fs/buffer.c b/fs/buffer.c
index 838c0c571022..33c3580b85d8 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -2241,14 +2241,18 @@ EXPORT_SYMBOL(block_commit_write);
  *
  * The filesystem needs to handle block truncation upon failure.
  */
-int block_write_begin(struct address_space *mapping, loff_t pos, unsigned len,
-		struct folio **foliop, get_block_t *get_block)
+int block_write_begin(const struct kiocb *iocb, struct address_space *mapping,
+		loff_t pos, unsigned len, struct folio **foliop, get_block_t *get_block)
 {
 	pgoff_t index = pos >> PAGE_SHIFT;
+	fgf_t fgp_flags = FGP_WRITEBEGIN;
 	struct folio *folio;
 	int status;
 
-	folio = __filemap_get_folio(mapping, index, FGP_WRITEBEGIN,
+	if (iocb && iocb->ki_flags & IOCB_DONTCACHE)
+		fgp_flags |= FGP_DONTCACHE;
+
+	folio = __filemap_get_folio(mapping, index, fgp_flags,
 			mapping_gfp_mask(mapping));
 	if (IS_ERR(folio))
 		return PTR_ERR(folio);
@@ -2591,7 +2595,7 @@ int cont_write_begin(const struct kiocb *iocb, struct address_space *mapping,
 		(*bytes)++;
 	}
 
-	return block_write_begin(mapping, pos, len, foliop, get_block);
+	return block_write_begin(iocb, mapping, pos, len, foliop, get_block);
 }
 EXPORT_SYMBOL(cont_write_begin);
 
diff --git a/fs/exfat/inode.c b/fs/exfat/inode.c
index f9501c3a3666..39d36e8fdfd6 100644
--- a/fs/exfat/inode.c
+++ b/fs/exfat/inode.c
@@ -456,7 +456,7 @@ static int exfat_write_begin(const struct kiocb *iocb,
 	if (unlikely(exfat_forced_shutdown(mapping->host->i_sb)))
 		return -EIO;
 
-	ret = block_write_begin(mapping, pos, len, foliop, exfat_get_block);
+	ret = block_write_begin(iocb, mapping, pos, len, foliop, exfat_get_block);
 
 	if (ret < 0)
 		exfat_write_failed(mapping, pos+len);
diff --git a/fs/ext2/inode.c b/fs/ext2/inode.c
index dbfe9098a124..11aab03de752 100644
--- a/fs/ext2/inode.c
+++ b/fs/ext2/inode.c
@@ -930,7 +930,7 @@ ext2_write_begin(const struct kiocb *iocb, struct address_space *mapping,
 {
 	int ret;
 
-	ret = block_write_begin(mapping, pos, len, foliop, ext2_get_block);
+	ret = block_write_begin(iocb, mapping, pos, len, foliop, ext2_get_block);
 	if (ret < 0)
 		ext2_write_failed(mapping, pos + len);
 	return ret;
diff --git a/fs/jfs/inode.c b/fs/jfs/inode.c
index 4709762713ef..ae52db437771 100644
--- a/fs/jfs/inode.c
+++ b/fs/jfs/inode.c
@@ -303,7 +303,7 @@ static int jfs_write_begin(const struct kiocb *iocb,
 {
 	int ret;
 
-	ret = block_write_begin(mapping, pos, len, foliop, jfs_get_block);
+	ret = block_write_begin(iocb, mapping, pos, len, foliop, jfs_get_block);
 	if (unlikely(ret))
 		jfs_write_failed(mapping, pos + len);
 
diff --git a/fs/minix/inode.c b/fs/minix/inode.c
index 51ea9bdc813f..9075c0ba2f20 100644
--- a/fs/minix/inode.c
+++ b/fs/minix/inode.c
@@ -465,7 +465,7 @@ static int minix_write_begin(const struct kiocb *iocb,
 {
 	int ret;
 
-	ret = block_write_begin(mapping, pos, len, foliop, minix_get_block);
+	ret = block_write_begin(iocb, mapping, pos, len, foliop, minix_get_block);
 	if (unlikely(ret))
 		minix_write_failed(mapping, pos + len);
 
diff --git a/fs/nilfs2/inode.c b/fs/nilfs2/inode.c
index 51bde45d5865..d9d57eeecc5d 100644
--- a/fs/nilfs2/inode.c
+++ b/fs/nilfs2/inode.c
@@ -230,7 +230,7 @@ static int nilfs_write_begin(const struct kiocb *iocb,
 	if (unlikely(err))
 		return err;
 
-	err = block_write_begin(mapping, pos, len, foliop, nilfs_get_block);
+	err = block_write_begin(iocb, mapping, pos, len, foliop, nilfs_get_block);
 	if (unlikely(err)) {
 		nilfs_write_failed(mapping, pos + len);
 		nilfs_transaction_abort(inode->i_sb);
diff --git a/fs/nilfs2/recovery.c b/fs/nilfs2/recovery.c
index a9c61d0492cb..2f5fe44bf736 100644
--- a/fs/nilfs2/recovery.c
+++ b/fs/nilfs2/recovery.c
@@ -541,7 +541,7 @@ static int nilfs_recover_dsync_blocks(struct the_nilfs *nilfs,
 		}
 
 		pos = rb->blkoff << inode->i_blkbits;
-		err = block_write_begin(inode->i_mapping, pos, blocksize,
+		err = block_write_begin(NULL, inode->i_mapping, pos, blocksize,
 					&folio, nilfs_get_block);
 		if (unlikely(err)) {
 			loff_t isize = inode->i_size;
diff --git a/fs/ntfs3/inode.c b/fs/ntfs3/inode.c
index 0a9ac5efeb67..8c788feb319e 100644
--- a/fs/ntfs3/inode.c
+++ b/fs/ntfs3/inode.c
@@ -966,7 +966,7 @@ int ntfs_write_begin(const struct kiocb *iocb, struct address_space *mapping,
 			goto out;
 	}
 
-	err = block_write_begin(mapping, pos, len, foliop,
+	err = block_write_begin(iocb, mapping, pos, len, foliop,
 				ntfs_get_block_write_begin);
 
 out:
diff --git a/fs/omfs/file.c b/fs/omfs/file.c
index 49a1de5a827f..3bade632e36e 100644
--- a/fs/omfs/file.c
+++ b/fs/omfs/file.c
@@ -317,7 +317,7 @@ static int omfs_write_begin(const struct kiocb *iocb,
 {
 	int ret;
 
-	ret = block_write_begin(mapping, pos, len, foliop, omfs_get_block);
+	ret = block_write_begin(iocb, mapping, pos, len, foliop, omfs_get_block);
 	if (unlikely(ret))
 		omfs_write_failed(mapping, pos + len);
 
diff --git a/fs/udf/inode.c b/fs/udf/inode.c
index 7fae8002344a..aec9cdc938be 100644
--- a/fs/udf/inode.c
+++ b/fs/udf/inode.c
@@ -259,7 +259,7 @@ static int udf_write_begin(const struct kiocb *iocb,
 	int ret;
 
 	if (iinfo->i_alloc_type != ICBTAG_FLAG_AD_IN_ICB) {
-		ret = block_write_begin(mapping, pos, len, foliop,
+		ret = block_write_begin(iocb, mapping, pos, len, foliop,
 					udf_get_block);
 		if (unlikely(ret))
 			udf_write_failed(mapping, pos + len);
diff --git a/fs/ufs/inode.c b/fs/ufs/inode.c
index e2b0a35de2a7..dfba985265a8 100644
--- a/fs/ufs/inode.c
+++ b/fs/ufs/inode.c
@@ -481,7 +481,7 @@ static int ufs_write_begin(const struct kiocb *iocb,
 {
 	int ret;
 
-	ret = block_write_begin(mapping, pos, len, foliop, ufs_getfrag_block);
+	ret = block_write_begin(iocb, mapping, pos, len, foliop, ufs_getfrag_block);
 	if (unlikely(ret))
 		ufs_write_failed(mapping, pos + len);
 
diff --git a/include/linux/buffer_head.h b/include/linux/buffer_head.h
index b16b88bfbc3e..4b07dec5f8eb 100644
--- a/include/linux/buffer_head.h
+++ b/include/linux/buffer_head.h
@@ -258,8 +258,9 @@ int __block_write_full_folio(struct inode *inode, struct folio *folio,
 		get_block_t *get_block, struct writeback_control *wbc);
 int block_read_full_folio(struct folio *, get_block_t *);
 bool block_is_partially_uptodate(struct folio *, size_t from, size_t count);
-int block_write_begin(struct address_space *mapping, loff_t pos, unsigned len,
-		struct folio **foliop, get_block_t *get_block);
+int block_write_begin(const struct kiocb *iocb, struct address_space *mapping,
+		loff_t pos, unsigned len, struct folio **foliop,
+		get_block_t *get_block);
 int __block_write_begin(struct folio *folio, loff_t pos, unsigned len,
 		get_block_t *get_block);
 int block_write_end(loff_t pos, unsigned len, unsigned copied, struct folio *);

---
base-commit: 05f7e89ab9731565d8a62e3b5d1ec206485eeb0b
change-id: 20260218-blk-dontcache-338133dd045e

Best regards,
-- 
Tal Zussman <tz2294@columbia.edu>

Re: [PATCH RFC] block: enable RWF_DONTCACHE for block devices

[Jan Kara]

On Wed 18-02-26 16:13:17, Tal Zussman wrote:
> Block device buffered reads and writes already pass through
> filemap_read() and iomap_file_buffered_write() respectively, both of
> which handle IOCB_DONTCACHE. Enable RWF_DONTCACHE for block device files
> by setting FOP_DONTCACHE in def_blk_fops.
> 
> For CONFIG_BUFFER_HEAD paths, thread the kiocb through
> block_write_begin() so that buffer_head-based I/O can use DONTCACHE
> behavior as well. Callers without a kiocb context (e.g. nilfs2 recovery)
> pass NULL, which preserves the existing behavior.
> 
> This support is useful for databases that operate on raw block devices,
> among other userspace applications.
> 
> Signed-off-by: Tal Zussman <tz2294@columbia.edu>

Looks good to me. Feel free to add:

Reviewed-by: Jan Kara <jack@suse.cz>

								Honza

> ---
> This is based on v6.19. Please let me know if there's a different tree I
> should base this on.
> 
> I wasn't sure if the block_write_begin() changes were necessary for
> block device support if CONFIG_BUFFER_HEAD is set (hence the RFC tag). I
> can remove those if they're not necessary.
> ---
>  block/fops.c                |  4 ++--
>  fs/bfs/file.c               |  2 +-
>  fs/buffer.c                 | 12 ++++++++----
>  fs/exfat/inode.c            |  2 +-
>  fs/ext2/inode.c             |  2 +-
>  fs/jfs/inode.c              |  2 +-
>  fs/minix/inode.c            |  2 +-
>  fs/nilfs2/inode.c           |  2 +-
>  fs/nilfs2/recovery.c        |  2 +-
>  fs/ntfs3/inode.c            |  2 +-
>  fs/omfs/file.c              |  2 +-
>  fs/udf/inode.c              |  2 +-
>  fs/ufs/inode.c              |  2 +-
>  include/linux/buffer_head.h |  5 +++--
>  14 files changed, 24 insertions(+), 19 deletions(-)
> 
> diff --git a/block/fops.c b/block/fops.c
> index 4d32785b31d9..6bc727f8b252 100644
> --- a/block/fops.c
> +++ b/block/fops.c
> @@ -505,7 +505,7 @@ static int blkdev_write_begin(const struct kiocb *iocb,
>  			      unsigned len, struct folio **foliop,
>  			      void **fsdata)
>  {
> -	return block_write_begin(mapping, pos, len, foliop, blkdev_get_block);
> +	return block_write_begin(iocb, mapping, pos, len, foliop, blkdev_get_block);
>  }
>  
>  static int blkdev_write_end(const struct kiocb *iocb,
> @@ -967,7 +967,7 @@ const struct file_operations def_blk_fops = {
>  	.splice_write	= iter_file_splice_write,
>  	.fallocate	= blkdev_fallocate,
>  	.uring_cmd	= blkdev_uring_cmd,
> -	.fop_flags	= FOP_BUFFER_RASYNC,
> +	.fop_flags	= FOP_BUFFER_RASYNC | FOP_DONTCACHE,
>  };
>  
>  static __init int blkdev_init(void)
> diff --git a/fs/bfs/file.c b/fs/bfs/file.c
> index d33d6bde992b..f2804e38b8a7 100644
> --- a/fs/bfs/file.c
> +++ b/fs/bfs/file.c
> @@ -177,7 +177,7 @@ static int bfs_write_begin(const struct kiocb *iocb,
>  {
>  	int ret;
>  
> -	ret = block_write_begin(mapping, pos, len, foliop, bfs_get_block);
> +	ret = block_write_begin(iocb, mapping, pos, len, foliop, bfs_get_block);
>  	if (unlikely(ret))
>  		bfs_write_failed(mapping, pos + len);
>  
> diff --git a/fs/buffer.c b/fs/buffer.c
> index 838c0c571022..33c3580b85d8 100644
> --- a/fs/buffer.c
> +++ b/fs/buffer.c
> @@ -2241,14 +2241,18 @@ EXPORT_SYMBOL(block_commit_write);
>   *
>   * The filesystem needs to handle block truncation upon failure.
>   */
> -int block_write_begin(struct address_space *mapping, loff_t pos, unsigned len,
> -		struct folio **foliop, get_block_t *get_block)
> +int block_write_begin(const struct kiocb *iocb, struct address_space *mapping,
> +		loff_t pos, unsigned len, struct folio **foliop, get_block_t *get_block)
>  {
>  	pgoff_t index = pos >> PAGE_SHIFT;
> +	fgf_t fgp_flags = FGP_WRITEBEGIN;
>  	struct folio *folio;
>  	int status;
>  
> -	folio = __filemap_get_folio(mapping, index, FGP_WRITEBEGIN,
> +	if (iocb && iocb->ki_flags & IOCB_DONTCACHE)
> +		fgp_flags |= FGP_DONTCACHE;
> +
> +	folio = __filemap_get_folio(mapping, index, fgp_flags,
>  			mapping_gfp_mask(mapping));
>  	if (IS_ERR(folio))
>  		return PTR_ERR(folio);
> @@ -2591,7 +2595,7 @@ int cont_write_begin(const struct kiocb *iocb, struct address_space *mapping,
>  		(*bytes)++;
>  	}
>  
> -	return block_write_begin(mapping, pos, len, foliop, get_block);
> +	return block_write_begin(iocb, mapping, pos, len, foliop, get_block);
>  }
>  EXPORT_SYMBOL(cont_write_begin);
>  
> diff --git a/fs/exfat/inode.c b/fs/exfat/inode.c
> index f9501c3a3666..39d36e8fdfd6 100644
> --- a/fs/exfat/inode.c
> +++ b/fs/exfat/inode.c
> @@ -456,7 +456,7 @@ static int exfat_write_begin(const struct kiocb *iocb,
>  	if (unlikely(exfat_forced_shutdown(mapping->host->i_sb)))
>  		return -EIO;
>  
> -	ret = block_write_begin(mapping, pos, len, foliop, exfat_get_block);
> +	ret = block_write_begin(iocb, mapping, pos, len, foliop, exfat_get_block);
>  
>  	if (ret < 0)
>  		exfat_write_failed(mapping, pos+len);
> diff --git a/fs/ext2/inode.c b/fs/ext2/inode.c
> index dbfe9098a124..11aab03de752 100644
> --- a/fs/ext2/inode.c
> +++ b/fs/ext2/inode.c
> @@ -930,7 +930,7 @@ ext2_write_begin(const struct kiocb *iocb, struct address_space *mapping,
>  {
>  	int ret;
>  
> -	ret = block_write_begin(mapping, pos, len, foliop, ext2_get_block);
> +	ret = block_write_begin(iocb, mapping, pos, len, foliop, ext2_get_block);
>  	if (ret < 0)
>  		ext2_write_failed(mapping, pos + len);
>  	return ret;
> diff --git a/fs/jfs/inode.c b/fs/jfs/inode.c
> index 4709762713ef..ae52db437771 100644
> --- a/fs/jfs/inode.c
> +++ b/fs/jfs/inode.c
> @@ -303,7 +303,7 @@ static int jfs_write_begin(const struct kiocb *iocb,
>  {
>  	int ret;
>  
> -	ret = block_write_begin(mapping, pos, len, foliop, jfs_get_block);
> +	ret = block_write_begin(iocb, mapping, pos, len, foliop, jfs_get_block);
>  	if (unlikely(ret))
>  		jfs_write_failed(mapping, pos + len);
>  
> diff --git a/fs/minix/inode.c b/fs/minix/inode.c
> index 51ea9bdc813f..9075c0ba2f20 100644
> --- a/fs/minix/inode.c
> +++ b/fs/minix/inode.c
> @@ -465,7 +465,7 @@ static int minix_write_begin(const struct kiocb *iocb,
>  {
>  	int ret;
>  
> -	ret = block_write_begin(mapping, pos, len, foliop, minix_get_block);
> +	ret = block_write_begin(iocb, mapping, pos, len, foliop, minix_get_block);
>  	if (unlikely(ret))
>  		minix_write_failed(mapping, pos + len);
>  
> diff --git a/fs/nilfs2/inode.c b/fs/nilfs2/inode.c
> index 51bde45d5865..d9d57eeecc5d 100644
> --- a/fs/nilfs2/inode.c
> +++ b/fs/nilfs2/inode.c
> @@ -230,7 +230,7 @@ static int nilfs_write_begin(const struct kiocb *iocb,
>  	if (unlikely(err))
>  		return err;
>  
> -	err = block_write_begin(mapping, pos, len, foliop, nilfs_get_block);
> +	err = block_write_begin(iocb, mapping, pos, len, foliop, nilfs_get_block);
>  	if (unlikely(err)) {
>  		nilfs_write_failed(mapping, pos + len);
>  		nilfs_transaction_abort(inode->i_sb);
> diff --git a/fs/nilfs2/recovery.c b/fs/nilfs2/recovery.c
> index a9c61d0492cb..2f5fe44bf736 100644
> --- a/fs/nilfs2/recovery.c
> +++ b/fs/nilfs2/recovery.c
> @@ -541,7 +541,7 @@ static int nilfs_recover_dsync_blocks(struct the_nilfs *nilfs,
>  		}
>  
>  		pos = rb->blkoff << inode->i_blkbits;
> -		err = block_write_begin(inode->i_mapping, pos, blocksize,
> +		err = block_write_begin(NULL, inode->i_mapping, pos, blocksize,
>  					&folio, nilfs_get_block);
>  		if (unlikely(err)) {
>  			loff_t isize = inode->i_size;
> diff --git a/fs/ntfs3/inode.c b/fs/ntfs3/inode.c
> index 0a9ac5efeb67..8c788feb319e 100644
> --- a/fs/ntfs3/inode.c
> +++ b/fs/ntfs3/inode.c
> @@ -966,7 +966,7 @@ int ntfs_write_begin(const struct kiocb *iocb, struct address_space *mapping,
>  			goto out;
>  	}
>  
> -	err = block_write_begin(mapping, pos, len, foliop,
> +	err = block_write_begin(iocb, mapping, pos, len, foliop,
>  				ntfs_get_block_write_begin);
>  
>  out:
> diff --git a/fs/omfs/file.c b/fs/omfs/file.c
> index 49a1de5a827f..3bade632e36e 100644
> --- a/fs/omfs/file.c
> +++ b/fs/omfs/file.c
> @@ -317,7 +317,7 @@ static int omfs_write_begin(const struct kiocb *iocb,
>  {
>  	int ret;
>  
> -	ret = block_write_begin(mapping, pos, len, foliop, omfs_get_block);
> +	ret = block_write_begin(iocb, mapping, pos, len, foliop, omfs_get_block);
>  	if (unlikely(ret))
>  		omfs_write_failed(mapping, pos + len);
>  
> diff --git a/fs/udf/inode.c b/fs/udf/inode.c
> index 7fae8002344a..aec9cdc938be 100644
> --- a/fs/udf/inode.c
> +++ b/fs/udf/inode.c
> @@ -259,7 +259,7 @@ static int udf_write_begin(const struct kiocb *iocb,
>  	int ret;
>  
>  	if (iinfo->i_alloc_type != ICBTAG_FLAG_AD_IN_ICB) {
> -		ret = block_write_begin(mapping, pos, len, foliop,
> +		ret = block_write_begin(iocb, mapping, pos, len, foliop,
>  					udf_get_block);
>  		if (unlikely(ret))
>  			udf_write_failed(mapping, pos + len);
> diff --git a/fs/ufs/inode.c b/fs/ufs/inode.c
> index e2b0a35de2a7..dfba985265a8 100644
> --- a/fs/ufs/inode.c
> +++ b/fs/ufs/inode.c
> @@ -481,7 +481,7 @@ static int ufs_write_begin(const struct kiocb *iocb,
>  {
>  	int ret;
>  
> -	ret = block_write_begin(mapping, pos, len, foliop, ufs_getfrag_block);
> +	ret = block_write_begin(iocb, mapping, pos, len, foliop, ufs_getfrag_block);
>  	if (unlikely(ret))
>  		ufs_write_failed(mapping, pos + len);
>  
> diff --git a/include/linux/buffer_head.h b/include/linux/buffer_head.h
> index b16b88bfbc3e..4b07dec5f8eb 100644
> --- a/include/linux/buffer_head.h
> +++ b/include/linux/buffer_head.h
> @@ -258,8 +258,9 @@ int __block_write_full_folio(struct inode *inode, struct folio *folio,
>  		get_block_t *get_block, struct writeback_control *wbc);
>  int block_read_full_folio(struct folio *, get_block_t *);
>  bool block_is_partially_uptodate(struct folio *, size_t from, size_t count);
> -int block_write_begin(struct address_space *mapping, loff_t pos, unsigned len,
> -		struct folio **foliop, get_block_t *get_block);
> +int block_write_begin(const struct kiocb *iocb, struct address_space *mapping,
> +		loff_t pos, unsigned len, struct folio **foliop,
> +		get_block_t *get_block);
>  int __block_write_begin(struct folio *folio, loff_t pos, unsigned len,
>  		get_block_t *get_block);
>  int block_write_end(loff_t pos, unsigned len, unsigned copied, struct folio *);
> 
> ---
> base-commit: 05f7e89ab9731565d8a62e3b5d1ec206485eeb0b
> change-id: 20260218-blk-dontcache-338133dd045e
> 
> Best regards,
> -- 
> Tal Zussman <tz2294@columbia.edu>
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR

Re: [PATCH RFC] block: enable RWF_DONTCACHE for block devices

[Jens Axboe]

On 2/18/26 2:13 PM, Tal Zussman wrote:
> Block device buffered reads and writes already pass through
> filemap_read() and iomap_file_buffered_write() respectively, both of
> which handle IOCB_DONTCACHE. Enable RWF_DONTCACHE for block device files
> by setting FOP_DONTCACHE in def_blk_fops.
> 
> For CONFIG_BUFFER_HEAD paths, thread the kiocb through
> block_write_begin() so that buffer_head-based I/O can use DONTCACHE
> behavior as well. Callers without a kiocb context (e.g. nilfs2 recovery)
> pass NULL, which preserves the existing behavior.
> 
> This support is useful for databases that operate on raw block devices,
> among other userspace applications.

OOO right now so I'll take a real look when I'm back, but when I
originally did this work, it's not the issue side that's the issue. It's
the pruning done from completion context, and you need to ensure that's
sane context for that (non-irq).

-- 
Jens Axboe

Re: [PATCH RFC] block: enable RWF_DONTCACHE for block devices

[Tal Zussman]

On Thu, Feb 19, 2026 at 10:24 AM Jens Axboe <axboe@kernel.dk> wrote:
> On 2/18/26 2:13 PM, Tal Zussman wrote:
> > Block device buffered reads and writes already pass through
> > filemap_read() and iomap_file_buffered_write() respectively, both of
> > which handle IOCB_DONTCACHE. Enable RWF_DONTCACHE for block device files
> > by setting FOP_DONTCACHE in def_blk_fops.
> >
> > For CONFIG_BUFFER_HEAD paths, thread the kiocb through
> > block_write_begin() so that buffer_head-based I/O can use DONTCACHE
> > behavior as well. Callers without a kiocb context (e.g. nilfs2 recovery)
> > pass NULL, which preserves the existing behavior.
> >
> > This support is useful for databases that operate on raw block devices,
> > among other userspace applications.
>
> OOO right now so I'll take a real look when I'm back, but when I
> originally did this work, it's not the issue side that's the issue. It's
> the pruning done from completion context, and you need to ensure that's
> sane context for that (non-irq).

Thanks for taking a look! That was very helpful feedback.
I sent out a v2 hopefully addressing that here:
https://lore.kernel.org/lkml/20260225-blk-dontcache-v2-0-70e7ac4f7108@columbia.edu/

> --
> Jens Axboe