aboutsummaryrefslogtreecommitdiff
path: root/Documentation/filesystems/vfs.txt
diff options
context:
space:
mode:
authorAl Viro <viro@zeniv.linux.org.uk>2011-03-16 09:07:58 -0400
committerAl Viro <viro@zeniv.linux.org.uk>2011-03-16 16:48:06 -0400
commit1a102ff92579edeff5e3d5d3c76ca49977898f00 (patch)
tree5585d724c8a996b770bb7a621563a7535a8c0496 /Documentation/filesystems/vfs.txt
parent011949811b946bd3b72fca71200f197c6168a5f8 (diff)
downloadlinux-linaro-stable-1a102ff92579edeff5e3d5d3c76ca49977898f00.tar.gz
vfs: bury ->get_sb()
This is an ex-parrot. Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Diffstat (limited to 'Documentation/filesystems/vfs.txt')
-rw-r--r--Documentation/filesystems/vfs.txt56
1 files changed, 32 insertions, 24 deletions
diff --git a/Documentation/filesystems/vfs.txt b/Documentation/filesystems/vfs.txt
index 94cf97b901d7..ef0714aa8e40 100644
--- a/Documentation/filesystems/vfs.txt
+++ b/Documentation/filesystems/vfs.txt
@@ -95,10 +95,11 @@ functions:
extern int unregister_filesystem(struct file_system_type *);
The passed struct file_system_type describes your filesystem. When a
-request is made to mount a device onto a directory in your filespace,
-the VFS will call the appropriate get_sb() method for the specific
-filesystem. The dentry for the mount point will then be updated to
-point to the root inode for the new filesystem.
+request is made to mount a filesystem onto a directory in your namespace,
+the VFS will call the appropriate mount() method for the specific
+filesystem. New vfsmount refering to the tree returned by ->mount()
+will be attached to the mountpoint, so that when pathname resolution
+reaches the mountpoint it will jump into the root of that vfsmount.
You can see all filesystems that are registered to the kernel in the
file /proc/filesystems.
@@ -107,14 +108,14 @@ file /proc/filesystems.
struct file_system_type
-----------------------
-This describes the filesystem. As of kernel 2.6.22, the following
+This describes the filesystem. As of kernel 2.6.39, the following
members are defined:
struct file_system_type {
const char *name;
int fs_flags;
- int (*get_sb) (struct file_system_type *, int,
- const char *, void *, struct vfsmount *);
+ struct dentry (*mount) (struct file_system_type *, int,
+ const char *, void *);
void (*kill_sb) (struct super_block *);
struct module *owner;
struct file_system_type * next;
@@ -128,11 +129,11 @@ struct file_system_type {
fs_flags: various flags (i.e. FS_REQUIRES_DEV, FS_NO_DCACHE, etc.)
- get_sb: the method to call when a new instance of this
+ mount: the method to call when a new instance of this
filesystem should be mounted
kill_sb: the method to call when an instance of this filesystem
- should be unmounted
+ should be shut down
owner: for internal VFS use: you should initialize this to THIS_MODULE in
most cases.
@@ -141,7 +142,7 @@ struct file_system_type {
s_lock_key, s_umount_key: lockdep-specific
-The get_sb() method has the following arguments:
+The mount() method has the following arguments:
struct file_system_type *fs_type: describes the filesystem, partly initialized
by the specific filesystem code
@@ -153,32 +154,39 @@ The get_sb() method has the following arguments:
void *data: arbitrary mount options, usually comes as an ASCII
string (see "Mount Options" section)
- struct vfsmount *mnt: a vfs-internal representation of a mount point
+The mount() method must return the root dentry of the tree requested by
+caller. An active reference to its superblock must be grabbed and the
+superblock must be locked. On failure it should return ERR_PTR(error).
-The get_sb() method must determine if the block device specified
-in the dev_name and fs_type contains a filesystem of the type the method
-supports. If it succeeds in opening the named block device, it initializes a
-struct super_block descriptor for the filesystem contained by the block device.
-On failure it returns an error.
+The arguments match those of mount(2) and their interpretation
+depends on filesystem type. E.g. for block filesystems, dev_name is
+interpreted as block device name, that device is opened and if it
+contains a suitable filesystem image the method creates and initializes
+struct super_block accordingly, returning its root dentry to caller.
+
+->mount() may choose to return a subtree of existing filesystem - it
+doesn't have to create a new one. The main result from the caller's
+point of view is a reference to dentry at the root of (sub)tree to
+be attached; creation of new superblock is a common side effect.
The most interesting member of the superblock structure that the
-get_sb() method fills in is the "s_op" field. This is a pointer to
+mount() method fills in is the "s_op" field. This is a pointer to
a "struct super_operations" which describes the next level of the
filesystem implementation.
-Usually, a filesystem uses one of the generic get_sb() implementations
-and provides a fill_super() method instead. The generic methods are:
+Usually, a filesystem uses one of the generic mount() implementations
+and provides a fill_super() callback instead. The generic variants are:
- get_sb_bdev: mount a filesystem residing on a block device
+ mount_bdev: mount a filesystem residing on a block device
- get_sb_nodev: mount a filesystem that is not backed by a device
+ mount_nodev: mount a filesystem that is not backed by a device
- get_sb_single: mount a filesystem which shares the instance between
+ mount_single: mount a filesystem which shares the instance between
all mounts
-A fill_super() method implementation has the following arguments:
+A fill_super() callback implementation has the following arguments:
- struct super_block *sb: the superblock structure. The method fill_super()
+ struct super_block *sb: the superblock structure. The callback
must initialize this properly.
void *data: arbitrary mount options, usually comes as an ASCII