Merge branch 'upstream-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jgarzi...

[pandora-kernel.git] / Documentation / filesystems / fuse.txt

diff --git a/Documentation/filesystems/fuse.txt b/Documentation/filesystems/fuse.txt
index 324df27..397a41a 100644 (file)
--- a/Documentation/filesystems/fuse.txt
+++ b/Documentation/filesystems/fuse.txt
@@ -51,6 +51,22 @@ homepage:
 
   http://fuse.sourceforge.net/
 
+Filesystem type
+~~~~~~~~~~~~~~~
+
+The filesystem type given to mount(2) can be one of the following:
+
+'fuse'
+
+  This is the usual way to mount a FUSE filesystem.  The first
+  argument of the mount system call may contain an arbitrary string,
+  which is not interpreted by the kernel.
+
+'fuseblk'
+
+  The filesystem is block device based.  The first argument of the
+  mount system call is interpreted as the name of the device.
+
 Mount options
 ~~~~~~~~~~~~~
 
@@ -78,8 +94,8 @@ Mount options
   filesystem is free to implement it's access policy or leave it to
   the underlying file access mechanism (e.g. in case of network
   filesystems).  This option enables permission checking, restricting
-  access based on file mode.  This is option is usually useful
-  together with the 'allow_other' mount option.
+  access based on file mode.  It is usually useful together with the
+  'allow_other' mount option.
 
 'allow_other'
 
@@ -94,6 +110,11 @@ Mount options
   The default is infinite.  Note that the size of read requests is
   limited anyway to 32 pages (which is 128kbyte on i386).
 
+'blksize=N'
+
+  Set the block size for the filesystem.  The default is 512.  This
+  option is only valid for 'fuseblk' type mounts.
+
 Control filesystem
 ~~~~~~~~~~~~~~~~~~
 
@@ -111,7 +132,7 @@ For each connection the following files exist within this directory:
 
  'waiting'
 
-  The number of requests which are waiting to be transfered to
+  The number of requests which are waiting to be transferred 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.
@@ -124,6 +145,46 @@ For each connection the following files exist within this directory:
 
 Only the owner of the mount may read or write these files.
 
+Interrupting filesystem operations
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+If a process issuing a FUSE filesystem request is interrupted, the
+following will happen:
+
+  1) If the request is not yet sent to userspace AND the signal is
+     fatal (SIGKILL or unhandled fatal signal), then the request is
+     dequeued and returns immediately.
+
+  2) If the request is not yet sent to userspace AND the signal is not
+     fatal, then an 'interrupted' flag is set for the request.  When
+     the request has been successfully transferred to userspace and
+     this flag is set, an INTERRUPT request is queued.
+
+  3) If the request is already sent to userspace, then an INTERRUPT
+     request is queued.
+
+INTERRUPT requests take precedence over other requests, so the
+userspace filesystem will receive queued INTERRUPTs before any others.
+
+The userspace filesystem may ignore the INTERRUPT requests entirely,
+or may honor them by sending a reply to the _original_ request, with
+the error set to EINTR.
+
+It is also possible that there's a race between processing the
+original request and it's INTERRUPT request.  There are two possibilities:
+
+  1) The INTERRUPT request is processed before the original request is
+     processed
+
+  2) The INTERRUPT request is processed after the original request has
+     been answered
+
+If the filesystem cannot find the original request, it should wait for
+some timeout and/or a number of new requests to arrive, after which it
+should reply to the INTERRUPT request with an EAGAIN error.  In case
+1) the INTERRUPT request will be requeued.  In case 2) the INTERRUPT
+reply will be ignored.
+
 Aborting a filesystem connection
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
@@ -351,10 +412,10 @@ but is caused by a pagefault.
 
 Solution is basically the same as above.
 
-An additional problem is that while the write buffer is being
-copied to the request, the request must not be interrupted.  This
-is because the destination address of the copy may not be valid
-after the request is interrupted.
+An additional problem is that while the write buffer is being copied
+to the request, the request must not be interrupted/aborted.  This is
+because the destination address of the copy may not be valid after the
+request has returned.
 
 This is solved with doing the copy atomically, and allowing abort
 while the page(s) belonging to the write buffer are faulted with