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-rw-r--r--Documentation/filesystems/fuse.txt48
1 files changed, 44 insertions, 4 deletions
diff --git a/Documentation/filesystems/fuse.txt b/Documentation/filesystems/fuse.txt
index 324df27..a584f05 100644
--- a/Documentation/filesystems/fuse.txt
+++ b/Documentation/filesystems/fuse.txt
@@ -124,6 +124,46 @@ 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 transfered 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 +391,10 @@ 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
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