From: Miklos Szeredi <miklos@szeredi.hu>
This adds lots of documentation for the userspace - kernel interface.
Signed-off-by: Miklos Szeredi <miklos@szeredi.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
---
fs/fuse/dev.c | 31 +++++++++++++++++++++++++++++--
1 files changed, 29 insertions(+), 2 deletions(-)
diff -puN fs/fuse/dev.c~fuse-mount-options-comments-and-documentation fs/fuse/dev.c
--- 25/fs/fuse/dev.c~fuse-mount-options-comments-and-documentation 2005-05-10 02:22:01.000000000 -0700
+++ 25-akpm/fs/fuse/dev.c 2005-05-10 02:22:01.000000000 -0700
@@ -198,10 +198,37 @@ static void request_end(struct fuse_conn
fuse_putback_request(fc, req);
}
+/*
+ * Unfortunately request interruption not just solves the deadlock
+ * problem, it causes problems too. These stem from the fact, that an
+ * interrupted request is continued to be processed in userspace,
+ * while all the locks and object references (inode and file) held
+ * during the operation are released.
+ *
+ * To release the locks is exactly why there's a need to interrupt the
+ * request, so there's not a lot that can be done about this, except
+ * introduce additional locking in userspace.
+ *
+ * More important is to keep inode and file references until userspace
+ * has replied, otherwise FORGET and RELEASE could be sent while the
+ * inode/file is still used by the filesystem.
+ *
+ * For this reason the concept of "background" request is introduced.
+ * An interrupted request is backgrounded if it has been already sent
+ * to userspace. Backgrounding involves getting an extra reference to
+ * inode(s) or file used in the request, and adding the request to
+ * fc->background list. When a reply is received for a background
+ * request, the object references are released, and the request is
+ * removed from the list. If the filesystem is unmounted while there
+ * are still background requests, the list is walked and references
+ * are released as if a reply was received.
+ *
+ * There's one more use for a background request. The RELEASE message is
+ * always sent as background, since it doesn't return an error or
+ * data.
+ */
static void background_request(struct fuse_conn *fc, struct fuse_req *req)
{
- /* Need to get hold of the inode(s) and/or file used in the
- request, so FORGET and RELEASE are not sent too early */
req->background = 1;
list_add(&req->bg_entry, &fc->background);
if (req->inode)
_