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authorDavid Howells <dhowells@redhat.com>2006-06-23 05:02:57 -0400
committerLinus Torvalds <torvalds@g5.osdl.org>2006-06-23 10:42:45 -0400
commit454e2398be9b9fa30433fccc548db34d19aa9958 (patch)
tree1f61cb0c3716a33b661cfc8977e9beeb480a322c /Documentation
parent1ad5544098a69d7dc1fa508cbb17e13a7a952fd8 (diff)
[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 <dhowells@redhat.com> Acked-by: Al Viro <viro@zeniv.linux.org.uk> Cc: Nathan Scott <nathans@sgi.com> Cc: Roland Dreier <rolandd@cisco.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/filesystems/Locking7
-rw-r--r--Documentation/filesystems/porting7
-rw-r--r--Documentation/filesystems/vfs.txt4
3 files changed, 10 insertions, 8 deletions
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.
142 142
143--------------------------- file_system_type --------------------------- 143--------------------------- file_system_type ---------------------------
144prototypes: 144prototypes:
145 struct super_block *(*get_sb) (struct file_system_type *, int, 145 struct int (*get_sb) (struct file_system_type *, int,
146 const char *, void *); 146 const char *, void *, struct vfsmount *);
147 void (*kill_sb) (struct super_block *); 147 void (*kill_sb) (struct super_block *);
148locking rules: 148locking rules:
149 may block BKL 149 may block BKL
150get_sb yes yes 150get_sb yes yes
151kill_sb yes yes 151kill_sb yes yes
152 152
153->get_sb() returns error or a locked superblock (exclusive on ->s_umount). 153->get_sb() returns error or 0 with locked superblock attached to the vfsmount
154(exclusive on ->s_umount).
154->kill_sb() takes a write-locked superblock, does all shutdown work on it, 155->kill_sb() takes a write-locked superblock, does all shutdown work on it,
155unlocks and drops the reference. 156unlocks and drops the reference.
156 157
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
50success and negative number in case of error (-EINVAL unless you have more 50success and negative number in case of error (-EINVAL unless you have more
51informative error value to report). Call it foo_fill_super(). Now declare 51informative error value to report). Call it foo_fill_super(). Now declare
52 52
53struct super_block foo_get_sb(struct file_system_type *fs_type, 53int foo_get_sb(struct file_system_type *fs_type,
54 int flags, const char *dev_name, void *data) 54 int flags, const char *dev_name, void *data, struct vfsmount *mnt)
55{ 55{
56 return get_sb_bdev(fs_type, flags, dev_name, data, ext2_fill_super); 56 return get_sb_bdev(fs_type, flags, dev_name, data, foo_fill_super,
57 mnt);
57} 58}
58 59
59(or similar with s/bdev/nodev/ or s/bdev/single/, depending on the kind of 60(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:
113struct file_system_type { 113struct file_system_type {
114 const char *name; 114 const char *name;
115 int fs_flags; 115 int fs_flags;
116 struct super_block *(*get_sb) (struct file_system_type *, int, 116 struct int (*get_sb) (struct file_system_type *, int,
117 const char *, void *); 117 const char *, void *, struct vfsmount *);
118 void (*kill_sb) (struct super_block *); 118 void (*kill_sb) (struct super_block *);
119 struct module *owner; 119 struct module *owner;
120 struct file_system_type * next; 120 struct file_system_type * next;