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fs: use backing_file container for internal files with "fake" f_path

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Overlayfs uses open_with_fake_path() to allocate internal kernel files,
with a "fake" path - whose f_path is not on the same fs as f_inode.

Allocate a container struct backing_file for those internal files, that
is used to hold the "fake" ovl path along with the real path.

backing_file_real_path() can be used to access the stored real path.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Message-Id: <20230615112229.2143178-5-amir73il@gmail.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>
This commit is contained in:
Amir Goldstein
2023-06-15 14:22:28 +03:00
committed by Christian Brauner
parent 8a05a8c31d
commit 62d53c4a1d
5 changed files with 114 additions and 23 deletions
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33
include/linux/fs.h
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@@ -171,6 +171,9 @@ typedef int (dio_iodone_t)(struct kiocb *iocb, loff_t offset,
/* File supports non-exclusive O_DIRECT writes from multiple threads */
#define FMODE_DIO_PARALLEL_WRITE ((__force fmode_t)0x1000000)
/* File is embedded in backing_file object */
#define FMODE_BACKING ((__force fmode_t)0x2000000)
/* File was opened by fanotify and shouldn't generate fanotify events */
#define FMODE_NONOTIFY ((__force fmode_t)0x4000000)
@@ -2352,11 +2355,31 @@ static inline struct file *file_open_root_mnt(struct vfsmount *mnt,
return file_open_root(&(struct path){.mnt = mnt, .dentry = mnt->mnt_root},
name, flags, mode);
}
extern struct file * dentry_open(const struct path *, int, const struct cred *);
extern struct file *dentry_create(const struct path *path, int flags,
umode_t mode, const struct cred *cred);
extern struct file * open_with_fake_path(const struct path *, int,
struct inode*, const struct cred *);
struct file *dentry_open(const struct path *path, int flags,
const struct cred *creds);
struct file *dentry_create(const struct path *path, int flags, umode_t mode,
const struct cred *cred);
struct file *backing_file_open(const struct path *path, int flags,
const struct path *real_path,
const struct cred *cred);
struct path *backing_file_real_path(struct file *f);
/*
* file_real_path - get the path corresponding to f_inode
*
* When opening a backing file for a stackable filesystem (e.g.,
* overlayfs) f_path may be on the stackable filesystem and f_inode on
* the underlying filesystem. When the path associated with f_inode is
* needed, this helper should be used instead of accessing f_path
* directly.
*/
static inline const struct path *file_real_path(struct file *f)
{
if (unlikely(f->f_mode & FMODE_BACKING))
return backing_file_real_path(f);
return &f->f_path;
}
static inline struct file *file_clone_open(struct file *file)
{
return dentry_open(&file->f_path, file->f_flags, file->f_cred);