On 09/14/2010 05:25 PM, Anthony Liguori wrote:
The incremental version of this is hard for me to understand.
bdrv_read() may be implemented in terms of bdrv_aio_read() +
qemu_io_wait() which dispatches bottom halves. This is done through a
shared resource so if you allow bdrv_read() to be called in parallel,
there's a very real possibility that you'll get corruption of a shared
resource.
You'd have to first instrument bdrv_read() to be re-entrant by
acquiring bs.mutex() in every bdrv_read() caller. You would then need
to modify the file protocol so that it could safely be called in
parallel.
IOW, you've got to make the whole block layer thread safe before you
can begin to make qcow2 thread safe.
It does rely on CONFIG_IO_THREAD and qemu_mutex. However, we don't need
to make the whole block layer safe, just the syncronous parts (drop
qemu_mutex after I/O is issued, rely on the image's mutex for internal
synchronization).
--
error compiling committee.c: too many arguments to function
