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| -rw-r--r-- | Documentation/filesystems/fuse.txt | 63 |
1 files changed, 63 insertions, 0 deletions
diff --git a/Documentation/filesystems/fuse.txt b/Documentation/filesystems/fuse.txt index 6b5741e651a2..33f74310d161 100644 --- a/Documentation/filesystems/fuse.txt +++ b/Documentation/filesystems/fuse.txt @@ -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->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. |