diff options
Diffstat (limited to 'Documentation/filesystems/porting')
-rw-r--r-- | Documentation/filesystems/porting | 69 |
1 files changed, 68 insertions, 1 deletions
diff --git a/Documentation/filesystems/porting b/Documentation/filesystems/porting index b12c8953868..07a32b42cf9 100644 --- a/Documentation/filesystems/porting +++ b/Documentation/filesystems/porting @@ -216,7 +216,6 @@ had ->revalidate()) add calls in ->follow_link()/->readlink(). ->d_parent changes are not protected by BKL anymore. Read access is safe if at least one of the following is true: * filesystem has no cross-directory rename() - * dcache_lock is held * we know that parent had been locked (e.g. we are looking at ->d_parent of ->lookup() argument). * we are called from ->rename(). @@ -318,3 +317,71 @@ if it's zero is not *and* *never* *had* *been* enough. Final unlink() and iput( may happen while the inode is in the middle of ->write_inode(); e.g. if you blindly free the on-disk inode, you may end up doing that while ->write_inode() is writing to it. + +--- +[mandatory] + + .d_delete() now only advises the dcache as to whether or not to cache +unreferenced dentries, and is now only called when the dentry refcount goes to +0. Even on 0 refcount transition, it must be able to tolerate being called 0, +1, or more times (eg. constant, idempotent). + +--- +[mandatory] + + .d_compare() calling convention and locking rules are significantly +changed. Read updated documentation in Documentation/filesystems/vfs.txt (and +look at examples of other filesystems) for guidance. + +--- +[mandatory] + + .d_hash() calling convention and locking rules are significantly +changed. Read updated documentation in Documentation/filesystems/vfs.txt (and +look at examples of other filesystems) for guidance. + +--- +[mandatory] + dcache_lock is gone, replaced by fine grained locks. See fs/dcache.c +for details of what locks to replace dcache_lock with in order to protect +particular things. Most of the time, a filesystem only needs ->d_lock, which +protects *all* the dcache state of a given dentry. + +-- +[mandatory] + + Filesystems must RCU-free their inodes, if they can have been accessed +via rcu-walk path walk (basically, if the file can have had a path name in the +vfs namespace). + + i_dentry and i_rcu share storage in a union, and the vfs expects +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. + + permission and check_acl are inode permission checks that are called +on many or all directory inodes on the way down a path walk (to check for +exec permission). These must now be rcu-walk aware (flags & IPERM_RCU). See +Documentation/filesystems/vfs.txt for more details. |