diff options
Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/filesystems/Locking | 18 | ||||
| -rw-r--r-- | Documentation/filesystems/path-lookup.txt | 5 | ||||
| -rw-r--r-- | Documentation/filesystems/porting | 20 | ||||
| -rw-r--r-- | Documentation/filesystems/vfs.txt | 9 |
4 files changed, 40 insertions, 12 deletions
diff --git a/Documentation/filesystems/Locking b/Documentation/filesystems/Locking index bdad6414dfa0..e90ffe61eb65 100644 --- a/Documentation/filesystems/Locking +++ b/Documentation/filesystems/Locking @@ -9,7 +9,7 @@ be able to use diff(1). --------------------------- dentry_operations -------------------------- prototypes: - int (*d_revalidate)(struct dentry *, int); + int (*d_revalidate)(struct dentry *, struct nameidata *); int (*d_hash)(const struct dentry *, const struct inode *, struct qstr *); int (*d_compare)(const struct dentry *, const struct inode *, @@ -21,14 +21,14 @@ prototypes: char *(*d_dname)((struct dentry *dentry, char *buffer, int buflen); locking rules: - rename_lock ->d_lock may block -d_revalidate: no no yes -d_hash no no no -d_compare: yes no no -d_delete: no yes no -d_release: no no yes -d_iput: no no yes -d_dname: no no no + rename_lock ->d_lock may block rcu-walk +d_revalidate: no no yes (ref-walk) maybe +d_hash no no no maybe +d_compare: yes no no maybe +d_delete: no yes no no +d_release: no no yes no +d_iput: no no yes no +d_dname: no no no no --------------------------- inode_operations --------------------------- prototypes: diff --git a/Documentation/filesystems/path-lookup.txt b/Documentation/filesystems/path-lookup.txt index 09b2878724a1..8789d1810bed 100644 --- a/Documentation/filesystems/path-lookup.txt +++ b/Documentation/filesystems/path-lookup.txt @@ -317,11 +317,10 @@ The detailed design for rcu-walk is like this: The cases where rcu-walk cannot continue are: * NULL dentry (ie. any uncached path element) * parent with d_inode->i_op->permission or ACLs -* dentries with d_revalidate * Following links -In future patches, permission checks and d_revalidate become rcu-walk aware. It -may be possible eventually to make following links rcu-walk aware. +In future patches, permission checks become rcu-walk aware. It may be possible +eventually to make following links rcu-walk aware. Uncached path elements will always require dropping to ref-walk mode, at the very least because i_mutex needs to be grabbed, and objects allocated. diff --git a/Documentation/filesystems/porting b/Documentation/filesystems/porting index ccf0ce7866b9..cd9756a2709d 100644 --- a/Documentation/filesystems/porting +++ b/Documentation/filesystems/porting @@ -360,3 +360,23 @@ i_dentry to be reinitialized before it is freed, so an: INIT_LIST_HEAD(&inode->i_dentry); must be done in the RCU callback. + +-- +[recommended] + vfs now tries to do path walking in "rcu-walk mode", which avoids +atomic operations and scalability hazards on dentries and inodes (see +Documentation/filesystems/path-walk.txt). d_hash and d_compare changes (above) +are examples of the changes required to support this. For more complex +filesystem callbacks, the vfs drops out of rcu-walk mode before the fs call, so +no changes are required to the filesystem. However, this is costly and loses +the benefits of rcu-walk mode. We will begin to add filesystem callbacks that +are rcu-walk aware, shown below. Filesystems should take advantage of this +where possible. + +-- +[mandatory] + d_revalidate is a callback that is made on every path element (if +the filesystem provides it), which requires dropping out of rcu-walk mode. This +may now be called in rcu-walk mode (nd->flags & LOOKUP_RCU). -ECHILD should be +returned if the filesystem cannot handle rcu-walk. See +Documentation/filesystems/vfs.txt for more details. diff --git a/Documentation/filesystems/vfs.txt b/Documentation/filesystems/vfs.txt index 69b10ff5ec81..c936b4912383 100644 --- a/Documentation/filesystems/vfs.txt +++ b/Documentation/filesystems/vfs.txt @@ -863,6 +863,15 @@ struct dentry_operations { dcache. Most filesystems leave this as NULL, because all their dentries in the dcache are valid + d_revalidate may be called in rcu-walk mode (nd->flags & LOOKUP_RCU). + If in rcu-walk mode, the filesystem must revalidate the dentry without + blocking or storing to the dentry, d_parent and d_inode should not be + used without care (because they can go NULL), instead nd->inode should + be used. + + If a situation is encountered that rcu-walk cannot handle, return + -ECHILD and it will be called again in ref-walk mode. + d_hash: called when the VFS adds a dentry to the hash table. The first dentry passed to d_hash is the parent directory that the name is to be hashed into. The inode is the dentry's inode. |