From 454e2398be9b9fa30433fccc548db34d19aa9958 Mon Sep 17 00:00:00 2001 From: David Howells Date: Fri, 23 Jun 2006 02:02:57 -0700 Subject: [PATCH] VFS: Permit filesystem to override root dentry on mount Extend the get_sb() filesystem operation to take an extra argument that permits the VFS to pass in the target vfsmount that defines the mountpoint. The filesystem is then required to manually set the superblock and root dentry pointers. For most filesystems, this should be done with simple_set_mnt() which will set the superblock pointer and then set the root dentry to the superblock's s_root (as per the old default behaviour). The get_sb() op now returns an integer as there's now no need to return the superblock pointer. This patch permits a superblock to be implicitly shared amongst several mount points, such as can be done with NFS to avoid potential inode aliasing. In such a case, simple_set_mnt() would not be called, and instead the mnt_root and mnt_sb would be set directly. The patch also makes the following changes: (*) the get_sb_*() convenience functions in the core kernel now take a vfsmount pointer argument and return an integer, so most filesystems have to change very little. (*) If one of the convenience function is not used, then get_sb() should normally call simple_set_mnt() to instantiate the vfsmount. This will always return 0, and so can be tail-called from get_sb(). (*) generic_shutdown_super() now calls shrink_dcache_sb() to clean up the dcache upon superblock destruction rather than shrink_dcache_anon(). This is required because the superblock may now have multiple trees that aren't actually bound to s_root, but that still need to be cleaned up. The currently called functions assume that the whole tree is rooted at s_root, and that anonymous dentries are not the roots of trees which results in dentries being left unculled. However, with the way NFS superblock sharing are currently set to be implemented, these assumptions are violated: the root of the filesystem is simply a dummy dentry and inode (the real inode for '/' may well be inaccessible), and all the vfsmounts are rooted on anonymous[*] dentries with child trees. [*] Anonymous until discovered from another tree. (*) The documentation has been adjusted, including the additional bit of changing ext2_* into foo_* in the documentation. [akpm@osdl.org: convert ipath_fs, do other stuff] Signed-off-by: David Howells Acked-by: Al Viro Cc: Nathan Scott Cc: Roland Dreier Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- Documentation/filesystems/Locking | 7 ++++--- Documentation/filesystems/porting | 7 ++++--- Documentation/filesystems/vfs.txt | 4 ++-- 3 files changed, 10 insertions(+), 8 deletions(-) (limited to 'Documentation') diff --git a/Documentation/filesystems/Locking b/Documentation/filesystems/Locking index 1045da582b9b..3abf08f1b14a 100644 --- a/Documentation/filesystems/Locking +++ b/Documentation/filesystems/Locking @@ -142,15 +142,16 @@ see also dquot_operations section. --------------------------- file_system_type --------------------------- prototypes: - struct super_block *(*get_sb) (struct file_system_type *, int, - const char *, void *); + struct int (*get_sb) (struct file_system_type *, int, + const char *, void *, struct vfsmount *); void (*kill_sb) (struct super_block *); locking rules: may block BKL get_sb yes yes kill_sb yes yes -->get_sb() returns error or a locked superblock (exclusive on ->s_umount). +->get_sb() returns error or 0 with locked superblock attached to the vfsmount +(exclusive on ->s_umount). ->kill_sb() takes a write-locked superblock, does all shutdown work on it, unlocks and drops the reference. diff --git a/Documentation/filesystems/porting b/Documentation/filesystems/porting index 2f388460cbe7..5531694059ab 100644 --- a/Documentation/filesystems/porting +++ b/Documentation/filesystems/porting @@ -50,10 +50,11 @@ Turn your foo_read_super() into a function that would return 0 in case of success and negative number in case of error (-EINVAL unless you have more informative error value to report). Call it foo_fill_super(). Now declare -struct super_block foo_get_sb(struct file_system_type *fs_type, - int flags, const char *dev_name, void *data) +int foo_get_sb(struct file_system_type *fs_type, + int flags, const char *dev_name, void *data, struct vfsmount *mnt) { - return get_sb_bdev(fs_type, flags, dev_name, data, ext2_fill_super); + return get_sb_bdev(fs_type, flags, dev_name, data, foo_fill_super, + mnt); } (or similar with s/bdev/nodev/ or s/bdev/single/, depending on the kind of diff --git a/Documentation/filesystems/vfs.txt b/Documentation/filesystems/vfs.txt index 3a2e5520c1e3..dd7d0dcedc87 100644 --- a/Documentation/filesystems/vfs.txt +++ b/Documentation/filesystems/vfs.txt @@ -113,8 +113,8 @@ members are defined: struct file_system_type { const char *name; int fs_flags; - struct super_block *(*get_sb) (struct file_system_type *, int, - const char *, void *); + struct int (*get_sb) (struct file_system_type *, int, + const char *, void *, struct vfsmount *); void (*kill_sb) (struct super_block *); struct module *owner; struct file_system_type * next; -- cgit v1.2.3