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[PATCH] fuse: update documentation for sysfs
Add documentation for new attributes in sysfs. Also describe the filesystem.
Signed-off-by: Miklos Szeredi <miklos@szeredi.hu>
Cc: Greg KH <greg@kroah.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
authored by Miklos Szeredi and committed by Linus Torvalds bacac382 c1aa96a5
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Documentation/filesystems/fuse.txt
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Documentation/filesystems/fuse.txt
···
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The default is infinite. Note that the size of read requests is
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limited anyway to 32 pages (which is 128kbyte on i386).
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Sysfs
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~~~~~
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FUSE sets up the following hierarchy in sysfs:
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/sys/fs/fuse/connections/N/
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where N is an increasing number allocated to each new connection.
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For each connection the following attributes are defined:
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'waiting'
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The number of requests which are waiting to be transfered to
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userspace or being processed by the filesystem daemon. If there is
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no filesystem activity and 'waiting' is non-zero, then the
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filesystem is hung or deadlocked.
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'abort'
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Writing anything into this file will abort the filesystem
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connection. This means that all waiting requests will be aborted an
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error returned for all aborted and new requests.
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Only a privileged user may read or write these attributes.
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Aborting a filesystem connection
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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It is possible to get into certain situations where the filesystem is
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not responding. Reasons for this may be:
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a) Broken userspace filesystem implementation
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b) Network connection down
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c) Accidental deadlock
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d) Malicious deadlock
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(For more on c) and d) see later sections)
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In either of these cases it may be useful to abort the connection to
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the filesystem. There are several ways to do this:
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- Kill the filesystem daemon. Works in case of a) and b)
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- Kill the filesystem daemon and all users of the filesystem. Works
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in all cases except some malicious deadlocks
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- Use forced umount (umount -f). Works in all cases but only if
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filesystem is still attached (it hasn't been lazy unmounted)
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- Abort filesystem through the sysfs interface. Most powerful
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method, always works.
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How do non-privileged mounts work?
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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···
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when the copy is taking place, and interruption is delayed until
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this flag is unset.
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Scenario 3 - Tricky deadlock with asynchronous read
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---------------------------------------------------
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The same situation as above, except thread-1 will wait on page lock
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and hence it will be uninterruptible as well. The solution is to
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abort the connection with forced umount (if mount is attached) or
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through the abort attribute in sysfs.