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authorMiklos Szeredi <miklos@szeredi.hu>2009-05-07 15:37:35 +0200
committerJens Axboe <jens.axboe@oracle.com>2009-05-11 14:13:09 +0200
commit7c77f0b3f9208c339a4b40737bb2cb0f0319bb8d (patch)
treecf45bc6afaa4bab28275b5aefc903f0112545965 /fs/coda
parentb1f744937f1be3e6d3009382a755679133cf782d (diff)
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splice: implement pipe to pipe splicing
Allow splice(2) to work when both the input and the output is a pipe. Based on the impementation of the tee(2) syscall, but instead of duplicating the buffer references move the buffers from the input pipe to the output pipe. Moving the whole buffer only succeeds if the full length of the buffer is spliced. Otherwise duplicate the buffer, just like tee(2), set the length of the output buffer and advance the offset on the input buffer. Since splice is operating on two pipes, special care needs to be taken with locking to prevent AN ABBA deadlock. Again this is done similarly to the tee(2) syscall, first preparing the input and output pipes so there's data to consume and space for that data, and then doing the move operation while holding both locks. If other processes are doing I/O on the same pipes parallel to the splice, then by the time both inodes are locked there might be no buffers left to move, or no space to move them to. In this case retry the whole operation, including the preparation phase. This could lead to starvation, but I'm not sure if that's serious enough to worry about. Signed-off-by: Miklos Szeredi <mszeredi@suse.cz> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
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