From ea5b778a8b98c85a87d66bf844904f9c3802b869 Mon Sep 17 00:00:00 2001 From: David Howells Date: Fri, 14 Jan 2011 19:10:03 +0000 Subject: Unexport do_add_mount() and add in follow_automount(), not ->d_automount() Unexport do_add_mount() and make ->d_automount() return the vfsmount to be added rather than calling do_add_mount() itself. follow_automount() will then do the addition. This slightly complicates things as ->d_automount() normally wants to add the new vfsmount to an expiration list and start an expiration timer. The problem with that is that the vfsmount will be deleted if it has a refcount of 1 and the timer will not repeat if the expiration list is empty. To this end, we require the vfsmount to be returned from d_automount() with a refcount of (at least) 2. One of these refs will be dropped unconditionally. In addition, follow_automount() must get a 3rd ref around the call to do_add_mount() lest it eat a ref and return an error, leaving the mount we have open to being expired as we would otherwise have only 1 ref on it. d_automount() should also add the the vfsmount to the expiration list (by calling mnt_set_expiry()) and start the expiration timer before returning, if this mechanism is to be used. The vfsmount will be unlinked from the expiration list by follow_automount() if do_add_mount() fails. This patch also fixes the call to do_add_mount() for AFS to propagate the mount flags from the parent vfsmount. Signed-off-by: David Howells Signed-off-by: Al Viro --- Documentation/filesystems/vfs.txt | 23 ++++++++++++++--------- 1 file changed, 14 insertions(+), 9 deletions(-) (limited to 'Documentation/filesystems') diff --git a/Documentation/filesystems/vfs.txt b/Documentation/filesystems/vfs.txt index 3c4b2f1b64d0..94cf97b901d7 100644 --- a/Documentation/filesystems/vfs.txt +++ b/Documentation/filesystems/vfs.txt @@ -933,15 +933,20 @@ struct dentry_operations { dynamic_dname() helper function is provided to take care of this. d_automount: called when an automount dentry is to be traversed (optional). - This should create a new VFS mount record, mount it on the directory - and return the record to the caller. The caller is supplied with a - path parameter giving the automount directory to describe the automount - target and the parent VFS mount record to provide inheritable mount - parameters. NULL should be returned if someone else managed to make - the automount first. If the automount failed, then an error code - should be returned. If -EISDIR is returned, then the directory will - be treated as an ordinary directory and returned to pathwalk to - continue walking. + This should create a new VFS mount record and return the record to the + caller. The caller is supplied with a path parameter giving the + automount directory to describe the automount target and the parent + VFS mount record to provide inheritable mount parameters. NULL should + be returned if someone else managed to make the automount first. If + the vfsmount creation failed, then an error code should be returned. + If -EISDIR is returned, then the directory will be treated as an + ordinary directory and returned to pathwalk to continue walking. + + If a vfsmount is returned, the caller will attempt to mount it on the + mountpoint and will remove the vfsmount from its expiration list in + the case of failure. The vfsmount should be returned with 2 refs on + it to prevent automatic expiration - the caller will clean up the + additional ref. This function is only used if DCACHE_NEED_AUTOMOUNT is set on the dentry. This is set by __d_instantiate() if S_AUTOMOUNT is set on the -- cgit v1.2.1