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List:       fuse-devel
Subject:    [fuse-devel] concurrent writes on the same file
From:       Sandeep Joshi <sanjos100 () gmail ! com>
Date:       2014-01-28 6:52:02
Message-ID: CAEfL3Kmv6BZ=wuduk6oOKsRZ5mgd-08iW1n3A3ky7XA8a06yAA () mail ! gmail ! com
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While doing some benchmarks with multiple threads, I saw that concurrent
writes on the same file are not possible with FUSE.

The number of outstanding iO seen in
/sys/fs/fuse/connections/<fsid>/waiting was always depressingly less than
expected.

I believe the reason for this is the mutex_lock on inode->i-mutex taken in
fuse_file_aio_write() in $kernel/fs/fuse/file.c

Is my reading of the code correct?  What is the lock protecting while the
IO has been sent to the userspace FUSE layer?   Is there a way to way to
*safely* allow concurrent writes on the same file.

thanks
-Sandeep
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