On Tue, Jul 09, 2013 at 09:05:06AM -0400, Jeff Layton wrote:
> On Wed, 3 Jul 2013 16:12:32 -0400
> "J. Bruce Fields" <bfields@xxxxxxxxxx> wrote:
>
> > From: "J. Bruce Fields" <bfields@xxxxxxxxxx>
> >
> > We need to break delegations on any operation that changes the set of
> > links pointing to an inode. Start with unlink.
> >
> > Such operations also hold the i_mutex on a parent directory. Breaking a
> > delegation may require waiting for a timeout (by default 90 seconds) in
> > the case of a unresponsive NFS client. To avoid blocking all directory
> > operations, we therefore drop locks before waiting for the delegation.
> > The logic then looks like:
> >
> > acquire locks
> > ...
> > test for delegation; if found:
> > take reference on inode
> > release locks
> > wait for delegation break
> > drop reference on inode
> > retry
> >
> > It is possible this could never terminate. (Even if we take precautions
> > to prevent another delegation being acquired on the same inode, we could
> > get a different inode on each retry.) But this seems very unlikely.
> >
> > The initial test for a delegation happens after the lock on the target
> > inode is acquired, but the directory inode may have been acquired
> > further up the call stack. We therefore add a "struct inode **"
> > argument to any intervening functions, which we use to pass the inode
> > back up to the caller in the case it needs a delegation synchronously
> > broken.
...
> > -int vfs_unlink(struct inode *dir, struct dentry *dentry)
> > +int vfs_unlink(struct inode *dir, struct dentry *dentry, struct inode **delegated_inode)
>
> nit: this might be a good time to add a kerneldoc header on this
> function. The delegated_inode thing might not be clear to the
> uninitiated.
Something like this?
--b.
diff --git a/fs/namei.c b/fs/namei.c
index cba3db1..7c6e244 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -3384,6 +3384,24 @@ SYSCALL_DEFINE1(rmdir, const char __user *, pathname)
return do_rmdir(AT_FDCWD, pathname);
}
+/**
+ * vfs_unlink - unlink a filesystem object
+ * @dir: parent directory
+ * @dentry: victim
+ * @delegated_inode: returns victim inode, if the inode is delegated.
+ *
+ * The caller must hold dir->i_mutex.
+ *
+ * If vfs_unlink discovers a delegation, it will return -EWOULDBLOCK and
+ * return a reference to the inode in delegated_inode. The caller
+ * should then break the delegation on that inode and retry. Because
+ * breaking a delegation may take a long time, the caller should drop
+ * dir->i_mutex before doing so.
+ *
+ * Alternatively, a caller may pass NULL for delegated_inode. This may
+ * be appropriate for callers that expect the underlying filesystem not
+ * to be NFS exported.
+ */
int vfs_unlink(struct inode *dir, struct dentry *dentry, struct inode **delegated_inode)
{
struct inode *target = dentry->d_inode;
--
To unsubscribe from this list: send the line "unsubscribe linux-nfs" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
