diff options
Diffstat (limited to 'Documentation/filesystems/vfs.rst')
| -rw-r--r-- | Documentation/filesystems/vfs.rst | 47 |
1 files changed, 44 insertions, 3 deletions
diff --git a/Documentation/filesystems/vfs.rst b/Documentation/filesystems/vfs.rst index 0b18af3f954e..ae79c30b6c0c 100644 --- a/Documentation/filesystems/vfs.rst +++ b/Documentation/filesystems/vfs.rst @@ -495,7 +495,7 @@ As of kernel 2.6.22, the following members are defined: int (*link) (struct dentry *,struct inode *,struct dentry *); int (*unlink) (struct inode *,struct dentry *); int (*symlink) (struct mnt_idmap *, struct inode *,struct dentry *,const char *); - int (*mkdir) (struct mnt_idmap *, struct inode *,struct dentry *,umode_t); + struct dentry *(*mkdir) (struct mnt_idmap *, struct inode *,struct dentry *,umode_t); int (*rmdir) (struct inode *,struct dentry *); int (*mknod) (struct mnt_idmap *, struct inode *,struct dentry *,umode_t,dev_t); int (*rename) (struct mnt_idmap *, struct inode *, struct dentry *, @@ -562,7 +562,26 @@ otherwise noted. ``mkdir`` called by the mkdir(2) system call. Only required if you want to support creating subdirectories. You will probably need to - call d_instantiate() just as you would in the create() method + call d_instantiate_new() just as you would in the create() method. + + If d_instantiate_new() is not used and if the fh_to_dentry() + export operation is provided, or if the storage might be + accessible by another path (e.g. with a network filesystem) + then more care may be needed. Importantly d_instantate() + should not be used with an inode that is no longer I_NEW if there + any chance that the inode could already be attached to a dentry. + This is because of a hard rule in the VFS that a directory must + only ever have one dentry. + + For example, if an NFS filesystem is mounted twice the new directory + could be visible on the other mount before it is on the original + mount, and a pair of name_to_handle_at(), open_by_handle_at() + calls could instantiate the directory inode with an IS_ROOT() + dentry before the first mkdir returns. + + If there is any chance this could happen, then the new inode + should be d_drop()ed and attached with d_splice_alias(). The + returned dentry (if any) should be returned by ->mkdir(). ``rmdir`` called by the rmdir(2) system call. Only required if you want @@ -1251,7 +1270,8 @@ defined: .. code-block:: c struct dentry_operations { - int (*d_revalidate)(struct dentry *, unsigned int); + int (*d_revalidate)(struct inode *, const struct qstr *, + struct dentry *, unsigned int); int (*d_weak_revalidate)(struct dentry *, unsigned int); int (*d_hash)(const struct dentry *, struct qstr *); int (*d_compare)(const struct dentry *, @@ -1264,6 +1284,8 @@ defined: struct vfsmount *(*d_automount)(struct path *); int (*d_manage)(const struct path *, bool); struct dentry *(*d_real)(struct dentry *, enum d_real_type type); + bool (*d_unalias_trylock)(const struct dentry *); + void (*d_unalias_unlock)(const struct dentry *); }; ``d_revalidate`` @@ -1427,6 +1449,25 @@ defined: For non-regular files, the 'dentry' argument is returned. +``d_unalias_trylock`` + if present, will be called by d_splice_alias() before moving a + preexisting attached alias. Returning false prevents __d_move(), + making d_splice_alias() fail with -ESTALE. + + Rationale: setting FS_RENAME_DOES_D_MOVE will prevent d_move() + and d_exchange() calls from the outside of filesystem methods; + however, it does not guarantee that attached dentries won't + be renamed or moved by d_splice_alias() finding a preexisting + alias for a directory inode. Normally we would not care; + however, something that wants to stabilize the entire path to + root over a blocking operation might need that. See 9p for one + (and hopefully only) example. + +``d_unalias_unlock`` + should be paired with ``d_unalias_trylock``; that one is called after + __d_move() call in __d_unalias(). + + Each dentry has a pointer to its parent dentry, as well as a hash list of child dentries. Child dentries are basically like files in a directory. |