[PATCH v2 01/34] bdev: open block device as files

Christian Brauner
2024-01-23T13:27:02Z

Add two new helpers to allow opening block devices as files.
This is not the final infrastructure. This still opens the block device
before opening a struct a file. Until we have removed all references to
struct bdev_handle we can't switch the order:

* Introduce blk_to_file_flags() to translate from block specific to
flags usable to pen a new file.
* Introduce bdev_file_open_by_{dev,path}().
* Introduce temporary sb_bdev_handle() helper to retrieve a struct
bdev_handle from a block device file and update places that directly
reference struct bdev_handle to rely on it.
* Don't count block device openes against the number of open files. A
bdev_file_open_by_{dev,path}() file is never installed into any
file descriptor table.

One idea that came to mind was to use kernel_tmpfile_open() which
would require us to pass a path and it would then call do_dentry_open()
going through the regular fops->open::blkdev_open() path. But that has
drawbacks that I consider fatal. We're back to the problem of
routing block specific flags such as BLK_OPEN_RESTRICT_WRITES through
the open path and would have to waste FMODE_* flags every time we add a
new one. Second, it would prohibit us from later using custom fops to
indicate that this is a restricted write operation as well. Overall, we
can avoid using an fmode flag and we have way more leeway in how we open
block devices from bdev_open_by_{dev,path}().

Signed-off-by: Christian Brauner <brauner@kernel.org>
---
block/bdev.c | 104 +++++++++++++++++++++++++++++++++++++++++++++++--
fs/cramfs/inode.c | 2 +-
fs/f2fs/super.c | 2 +-
fs/file_table.c | 36 +++++++++++++----
fs/jfs/jfs_logmgr.c | 2 +-
fs/romfs/super.c | 2 +-
fs/super.c | 18 ++++-----
fs/xfs/xfs_super.c | 2 +-
include/linux/blkdev.h | 7 ++++
include/linux/file.h | 2 +
include/linux/fs.h | 10 ++++-
11 files changed, 160 insertions(+), 27 deletions(-)

diff --git a/block/bdev.c b/block/bdev.c
index e9f1b12bd75c..4246a57a7c5a 100644
--- a/block/bdev.c
+++ b/block/bdev.c
@@ -49,6 +49,13 @@ struct block_device *I_BDEV(struct inode *inode)
}
EXPORT_SYMBOL(I_BDEV);

+struct block_device *file_bdev(struct file *bdev_file)
+{
+ struct bdev_handle *handle = bdev_file->private_data;
+ return handle->bdev;
+}
+EXPORT_SYMBOL(file_bdev);
+
static void bdev_write_inode(struct block_device *bdev)
{
struct inode *inode = bdev->bd_inode;
@@ -368,12 +375,12 @@ static struct file_system_type bd_type = {
};

struct super_block *blockdev_superblock __ro_after_init;
+struct vfsmount *blockdev_mnt __ro_after_init;
EXPORT_SYMBOL_GPL(blockdev_superblock);

void __init bdev_cache_init(void)
{
int err;
- static struct vfsmount *bd_mnt __ro_after_init;

bdev_cachep = kmem_cache_create("bdev_cache", sizeof(struct bdev_inode),
0, (SLAB_HWCACHE_ALIGN|SLAB_RECLAIM_ACCOUNT|
@@ -382,10 +389,10 @@ void __init bdev_cache_init(void)
err = register_filesystem(&bd_type);
if (err)
panic("Cannot register bdev pseudo-fs");
- bd_mnt = kern_mount(&bd_type);
- if (IS_ERR(bd_mnt))
+ blockdev_mnt = kern_mount(&bd_type);
+ if (IS_ERR(blockdev_mnt))
panic("Cannot create bdev pseudo-fs");
- blockdev_superblock = bd_mnt->mnt_sb; /* For writeback */
+ blockdev_superblock = blockdev_mnt->mnt_sb; /* For writeback */
}

struct block_device *bdev_alloc(struct gendisk *disk, u8 partno)
@@ -911,6 +918,95 @@ struct bdev_handle *bdev_open_by_dev(dev_t dev, blk_mode_t mode, void *holder,
}
EXPORT_SYMBOL(bdev_open_by_dev);

+static unsigned blk_to_file_flags(blk_mode_t mode)
+{
+ unsigned int flags = 0;
+
+ if ((mode & (BLK_OPEN_READ | BLK_OPEN_WRITE)) ==
+ (BLK_OPEN_READ | BLK_OPEN_WRITE))
+ flags |= O_RDWR;
+ else if (mode & BLK_OPEN_WRITE)
+ flags |= O_WRONLY;
+ else if (mode & BLK_OPEN_READ)
+ flags |= O_RDONLY;
+ else /* Neither read nor write for a block device requested? */
+ WARN_ON_ONCE(true);
+
+ /*
+ * O_EXCL is one of those flags that the VFS clears once it's done with
+ * the operation. So don't raise it here either.
+ */
+ if (mode & BLK_OPEN_NDELAY)
+ flags |= O_NDELAY;
+
+ /*
+ * If BLK_OPEN_WRITE_IOCTL is set then this is a historical quirk
+ * associated with the floppy driver where it has allowed ioctls if the
+ * file was opened for writing, but does not allow reads or writes.
+ * Make sure that this quirk is reflected in @f_flags.
+ */
+ if (mode & BLK_OPEN_WRITE_IOCTL)
+ flags |= O_RDWR | O_WRONLY;
+
+ return flags;
+}
+
+struct file *bdev_file_open_by_dev(dev_t dev, blk_mode_t mode, void *holder,
+ const struct blk_holder_ops *hops)
+{
+ struct file *bdev_file;
+ struct bdev_handle *handle;
+ unsigned int flags;
+
+ handle = bdev_open_by_dev(dev, mode, holder, hops);
+ if (IS_ERR(handle))
+ return ERR_CAST(handle);
+
+ flags = blk_to_file_flags(mode);
+ bdev_file = alloc_file_pseudo_noaccount(handle->bdev->bd_inode,
+ blockdev_mnt, "", flags | O_LARGEFILE, &def_blk_fops);
+ if (IS_ERR(bdev_file)) {
+ bdev_release(handle);
+ return bdev_file;
+ }
+ ihold(handle->bdev->bd_inode);
+
+ bdev_file->f_mode |= FMODE_BUF_RASYNC | FMODE_CAN_ODIRECT;
+ if (bdev_nowait(handle->bdev))
+ bdev_file->f_mode |= FMODE_NOWAIT;
+
+ bdev_file->f_mapping = handle->bdev->bd_inode->i_mapping;
+ bdev_file->f_wb_err = filemap_sample_wb_err(bdev_file->f_mapping);
+ bdev_file->private_data = handle;
+ return bdev_file;
+}
+EXPORT_SYMBOL(bdev_file_open_by_dev);
+
+struct file *bdev_file_open_by_path(const char *path, blk_mode_t mode,
+ void *holder,
+ const struct blk_holder_ops *hops)
+{
+ struct file *bdev_file;
+ dev_t dev;
+ int error;
+
+ error = lookup_bdev(path, &dev);
+ if (error)
+ return ERR_PTR(error);
+
+ bdev_file = bdev_file_open_by_dev(dev, mode, holder, hops);
+ if (!IS_ERR(bdev_file) && (mode & BLK_OPEN_WRITE)) {
+ struct bdev_handle *handle = bdev_file->private_data;
+ if (bdev_read_only(handle->bdev)) {
+ fput(bdev_file);
+ bdev_file = ERR_PTR(-EACCES);
+ }
+ }
+
+ return bdev_file;
+}
+EXPORT_SYMBOL(bdev_file_open_by_path);
+
/**
* bdev_open_by_path - open a block device by name
* @path: path to the block device to open
diff --git a/fs/cramfs/inode.c b/fs/cramfs/inode.c
index 60dbfa0f8805..39e75131fd5a 100644
--- a/fs/cramfs/inode.c
+++ b/fs/cramfs/inode.c
@@ -495,7 +495,7 @@ static void cramfs_kill_sb(struct super_block *sb)
sb->s_mtd = NULL;
} else if (IS_ENABLED(CONFIG_CRAMFS_BLOCKDEV) && sb->s_bdev) {
sync_blockdev(sb->s_bdev);
- bdev_release(sb->s_bdev_handle);
+ fput(sb->s_bdev_file);
}
kfree(sbi);
}
diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
index d45ab0992ae5..ea94c148fee5 100644
--- a/fs/f2fs/super.c
+++ b/fs/f2fs/super.c
@@ -4247,7 +4247,7 @@ static int f2fs_scan_devices(struct f2fs_sb_info *sbi)

for (i = 0; i < max_devices; i++) {
if (i == 0)
- FDEV(0).bdev_handle = sbi->sb->s_bdev_handle;
+ FDEV(0).bdev_handle = sb_bdev_handle(sbi->sb);
else if (!RDEV(i).path[0])
break;

diff --git a/fs/file_table.c b/fs/file_table.c
index b991f90571b4..f61e212b99f4 100644
--- a/fs/file_table.c
+++ b/fs/file_table.c
@@ -281,13 +281,17 @@ struct file *alloc_empty_backing_file(int flags, const struct cred *cred)
* @path: the (dentry, vfsmount) pair for the new file
* @flags: O_... flags with which the new file will be opened
* @fop: the 'struct file_operations' for the new file
+ * @noaccount: whether this is an internal open that shouldn't be counted
*/
static struct file *alloc_file(const struct path *path, int flags,
- const struct file_operations *fop)
+ const struct file_operations *fop, bool noaccount)
{
struct file *file;

- file = alloc_empty_file(flags, current_cred());
+ if (noaccount)
+ file = alloc_empty_file_noaccount(flags, current_cred());
+ else
+ file = alloc_empty_file(flags, current_cred());
if (IS_ERR(file))
return file;

@@ -312,9 +316,11 @@ static struct file *alloc_file(const struct path *path, int flags,
return file;
}

-struct file *alloc_file_pseudo(struct inode *inode, struct vfsmount *mnt,
- const char *name, int flags,
- const struct file_operations *fops)
+static struct file *__alloc_file_pseudo(struct inode *inode,
+ struct vfsmount *mnt, const char *name,
+ int flags,
+ const struct file_operations *fops,
+ bool noaccount)
{
struct qstr this = QSTR_INIT(name, strlen(name));
struct path path;
@@ -325,19 +331,35 @@ struct file *alloc_file_pseudo(struct inode *inode, struct vfsmount *mnt,
return ERR_PTR(-ENOMEM);
path.mnt = mntget(mnt);
d_instantiate(path.dentry, inode);
- file = alloc_file(&path, flags, fops);
+ file = alloc_file(&path, flags, fops, noaccount);
if (IS_ERR(file)) {
ihold(inode);
path_put(&path);
}
return file;
}
+
+struct file *alloc_file_pseudo(struct inode *inode, struct vfsmount *mnt,
+ const char *name, int flags,
+ const struct file_operations *fops)
+{
+ return __alloc_file_pseudo(inode, mnt, name, flags, fops, false);
+}
EXPORT_SYMBOL(alloc_file_pseudo);

+struct file *alloc_file_pseudo_noaccount(struct inode *inode,
+ struct vfsmount *mnt, const char *name,
+ int flags,
+ const struct file_operations *fops)
+{
+ return __alloc_file_pseudo(inode, mnt, name, flags, fops, true);
+}
+EXPORT_SYMBOL_GPL(alloc_file_pseudo_noaccount);
+
struct file *alloc_file_clone(struct file *base, int flags,
const struct file_operations *fops)
{
- struct file *f = alloc_file(&base->f_path, flags, fops);
+ struct file *f = alloc_file(&base->f_path, flags, fops, false);
if (!IS_ERR(f)) {
path_get(&f->f_path);
f->f_mapping = base->f_mapping;
diff --git a/fs/jfs/jfs_logmgr.c b/fs/jfs/jfs_logmgr.c
index cb6d1fda66a7..8691463956d1 100644
--- a/fs/jfs/jfs_logmgr.c
+++ b/fs/jfs/jfs_logmgr.c
@@ -1162,7 +1162,7 @@ static int open_inline_log(struct super_block *sb)
init_waitqueue_head(&log->syncwait);

set_bit(log_INLINELOG, &log->flag);
- log->bdev_handle = sb->s_bdev_handle;
+ log->bdev_handle = sb_bdev_handle(sb);
log->base = addressPXD(&JFS_SBI(sb)->logpxd);
log->size = lengthPXD(&JFS_SBI(sb)->logpxd) >>
(L2LOGPSIZE - sb->s_blocksize_bits);
diff --git a/fs/romfs/super.c b/fs/romfs/super.c
index 545ad44f96b8..1ed468c03557 100644
--- a/fs/romfs/super.c
+++ b/fs/romfs/super.c
@@ -594,7 +594,7 @@ static void romfs_kill_sb(struct super_block *sb)
#ifdef CONFIG_ROMFS_ON_BLOCK
if (sb->s_bdev) {
sync_blockdev(sb->s_bdev);
- bdev_release(sb->s_bdev_handle);
+ fput(sb->s_bdev_file);
}
#endif
}
diff --git a/fs/super.c b/fs/super.c
index d35e85295489..08dcc3371aa0 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -1532,16 +1532,16 @@ int setup_bdev_super(struct super_block *sb, int sb_flags,
struct fs_context *fc)
{
blk_mode_t mode = sb_open_mode(sb_flags);
- struct bdev_handle *bdev_handle;
+ struct file *bdev_file;
struct block_device *bdev;

- bdev_handle = bdev_open_by_dev(sb->s_dev, mode, sb, &fs_holder_ops);
- if (IS_ERR(bdev_handle)) {
+ bdev_file = bdev_file_open_by_dev(sb->s_dev, mode, sb, &fs_holder_ops);
+ if (IS_ERR(bdev_file)) {
if (fc)
errorf(fc, "%s: Can't open blockdev", fc->source);
- return PTR_ERR(bdev_handle);
+ return PTR_ERR(bdev_file);
}
- bdev = bdev_handle->bdev;
+ bdev = file_bdev(bdev_file);

/*
* This really should be in blkdev_get_by_dev, but right now can't due
@@ -1549,7 +1549,7 @@ int setup_bdev_super(struct super_block *sb, int sb_flags,
* writable from userspace even for a read-only block device.
*/
if ((mode & BLK_OPEN_WRITE) && bdev_read_only(bdev)) {
- bdev_release(bdev_handle);
+ fput(bdev_file);
return -EACCES;
}

@@ -1560,11 +1560,11 @@ int setup_bdev_super(struct super_block *sb, int sb_flags,
if (atomic_read(&bdev->bd_fsfreeze_count) > 0) {
if (fc)
warnf(fc, "%pg: Can't mount, blockdev is frozen", bdev);
- bdev_release(bdev_handle);
+ fput(bdev_file);
return -EBUSY;
}
spin_lock(&sb_lock);
- sb->s_bdev_handle = bdev_handle;
+ sb->s_bdev_file = bdev_file;
sb->s_bdev = bdev;
sb->s_bdi = bdi_get(bdev->bd_disk->bdi);
if (bdev_stable_writes(bdev))
@@ -1680,7 +1680,7 @@ void kill_block_super(struct super_block *sb)
generic_shutdown_super(sb);
if (bdev) {
sync_blockdev(bdev);
- bdev_release(sb->s_bdev_handle);
+ fput(sb->s_bdev_file);
}
}

diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
index aff20ddd4a9f..e5ac0e59ede9 100644
--- a/fs/xfs/xfs_super.c
+++ b/fs/xfs/xfs_super.c
@@ -467,7 +467,7 @@ xfs_open_devices(
* Setup xfs_mount buffer target pointers
*/
error = -ENOMEM;
- mp->m_ddev_targp = xfs_alloc_buftarg(mp, sb->s_bdev_handle);
+ mp->m_ddev_targp = xfs_alloc_buftarg(mp, sb_bdev_handle(sb));
if (!mp->m_ddev_targp)
goto out_close_rtdev;

diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 99e4f5e72213..76706aa47316 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -24,6 +24,7 @@
#include <linux/sbitmap.h>
#include <linux/uuid.h>
#include <linux/xarray.h>
+#include <linux/file.h>

struct module;
struct request_queue;
@@ -1474,6 +1475,7 @@ extern const struct blk_holder_ops fs_holder_ops;
(BLK_OPEN_READ | BLK_OPEN_RESTRICT_WRITES | \
(((flags) & SB_RDONLY) ? 0 : BLK_OPEN_WRITE))

+/* @bdev_handle will be removed soon. */
struct bdev_handle {
struct block_device *bdev;
void *holder;
@@ -1484,6 +1486,10 @@ struct bdev_handle *bdev_open_by_dev(dev_t dev, blk_mode_t mode, void *holder,
const struct blk_holder_ops *hops);
struct bdev_handle *bdev_open_by_path(const char *path, blk_mode_t mode,
void *holder, const struct blk_holder_ops *hops);
+struct file *bdev_file_open_by_dev(dev_t dev, blk_mode_t mode, void *holder,
+ const struct blk_holder_ops *hops);
+struct file *bdev_file_open_by_path(const char *path, blk_mode_t mode,
+ void *holder, const struct blk_holder_ops *hops);
int bd_prepare_to_claim(struct block_device *bdev, void *holder,
const struct blk_holder_ops *hops);
void bd_abort_claiming(struct block_device *bdev, void *holder);
@@ -1494,6 +1500,7 @@ struct block_device *blkdev_get_no_open(dev_t dev);
void blkdev_put_no_open(struct block_device *bdev);

struct block_device *I_BDEV(struct inode *inode);
+struct block_device *file_bdev(struct file *bdev_file);

#ifdef CONFIG_BLOCK
void invalidate_bdev(struct block_device *bdev);
diff --git a/include/linux/file.h b/include/linux/file.h
index 6834a29338c4..169692cb1906 100644
--- a/include/linux/file.h
+++ b/include/linux/file.h
@@ -24,6 +24,8 @@ struct inode;
struct path;
extern struct file *alloc_file_pseudo(struct inode *, struct vfsmount *,
const char *, int flags, const struct file_operations *);
+extern struct file *alloc_file_pseudo_noaccount(struct inode *, struct vfsmount *,
+ const char *, int flags, const struct file_operations *);
extern struct file *alloc_file_clone(struct file *, int flags,
const struct file_operations *);

diff --git a/include/linux/fs.h b/include/linux/fs.h
index ed5966a70495..e9291e27cc47 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1228,8 +1228,8 @@ struct super_block {
#endif
struct hlist_bl_head s_roots; /* alternate root dentries for NFS */
struct list_head s_mounts; /* list of mounts; _not_ for fs use */
- struct block_device *s_bdev;
- struct bdev_handle *s_bdev_handle;
+ struct block_device *s_bdev; /* can go away once we use an accessor for @s_bdev_file */
+ struct file *s_bdev_file;
struct backing_dev_info *s_bdi;
struct mtd_info *s_mtd;
struct hlist_node s_instances;
@@ -1327,6 +1327,12 @@ struct super_block {
struct list_head s_inodes_wb; /* writeback inodes */
} __randomize_layout;

+/* Temporary helper that will go away. */
+static inline struct bdev_handle *sb_bdev_handle(struct super_block *sb)
+{
+ return sb->s_bdev_file->private_data;
+}
+
static inline struct user_namespace *i_user_ns(const struct inode *inode)
{
return inode->i_sb->s_user_ns;

--
2.43.0