Add documentation for new attributes in sysfs. Also describe the
different ways a connection may be aborted to a hung or deadlocked
filesystem.
Signed-off-by: Miklos Szeredi <[email protected]>
Index: linux/Documentation/filesystems/fuse.txt
===================================================================
--- linux.orig/Documentation/filesystems/fuse.txt 2006-01-03 04:21:10.000000000 +0100
+++ linux/Documentation/filesystems/fuse.txt 2006-01-14 01:31:13.000000000 +0100
@@ -86,6 +86,62 @@ Mount options
The default is infinite. Note that the size of read requests is
limited anyway to 32 pages (which is 128kbyte on i386).
+Sysfs
+~~~~~
+
+FUSE sets up the following hierarchy in sysfs:
+
+ /sys/fs/fuse/connections/N/
+
+where N is an increasing number allocated to each new connection.
+
+For each connection the following attributes are defined:
+
+ 'waiting'
+
+ The number of requests which are waiting to be transfered to
+ userspace or being processed by the filesystem daemon. If there is
+ no filesystem activity and 'waiting' is non-zero, then the
+ filesystem is hung or deadlocked.
+
+ 'abort'
+
+ Writing anything into this file will abort the filesystem
+ connection. This means that all waiting requests will be aborted an
+ error returned for all aborted and new requests.
+
+Only a privileged user may read or write these attributes.
+
+Aborting a filesystem connection
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+It is possible to get into certain situations where the filesystem is
+not responding. Reasons for this may be:
+
+ a) Broken userspace filesystem implementation
+
+ b) Network connection down
+
+ c) Accidental deadlock
+
+ d) Malicious deadlock
+
+(For more on c) and d) see later sections)
+
+In either of these cases it may be useful to abort the connection to
+the filesystem. There are several ways to do this:
+
+ - Kill the filesystem daemon. Works in case of a) and b)
+
+ - Kill the filesystem daemon and all users of the filesystem. Works
+ in all cases except some malicious deadlocks
+
+ - Use forced umount (umount -f). Works in all cases but only if
+ filesystem is still attached (it hasn't been lazy unmounted)
+
+ - Abort filesystem through the sysfs interface. Most powerful
+ method, always works.
+
How do non-privileged mounts work?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
@@ -313,3 +369,10 @@ faulted with get_user_pages(). The 'req
when the copy is taking place, and interruption is delayed until
this flag is unset.
+Scenario 3 - Tricky deadlock with asynchronous read
+---------------------------------------------------
+
+The same situation as above, except thread-1 will wait on page lock
+and hence it will be uninterruptible as well. The solution is to
+abort the connection with forced umount (if mount is attached) or
+through the abort attribute in sysfs.
--
-
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