Commit bacac382 authored by Miklos Szeredi's avatar Miklos Szeredi Committed by Linus Torvalds
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[PATCH] fuse: update documentation for sysfs

Add documentation for new attributes in sysfs.  Also describe the filesystem.
Signed-off-by: default avatarMiklos Szeredi <>
Cc: Greg KH <>
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent c1aa96a5
......@@ -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).
FUSE sets up the following hierarchy in sysfs:
where N is an increasing number allocated to each new connection.
For each connection the following attributes are defined:
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.
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->locked' flag indicates
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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