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author | Paolo Bonzini <pbonzini@redhat.com> | 2011-10-20 13:16:21 +0200 |
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committer | Kevin Wolf <kwolf@redhat.com> | 2011-10-21 17:34:13 +0200 |
commit | 848c66e8f5b631961580f7f010a5831430dc84c2 (patch) | |
tree | 4d6f47f0487b80669eca7185842849706d12b8d5 /qdict.c | |
parent | bae0a0cc38d324c83ba737b92215f3447981d73b (diff) |
block: add a CoMutex to synchronous read drivers
The big conversion of bdrv_read/write to coroutines caused the two
homonymous callbacks in BlockDriver to become reentrant. It goes
like this:
1) bdrv_read is now called in a coroutine, and calls bdrv_read or
bdrv_pread.
2) the nested bdrv_read goes through the fast path in bdrv_rw_co_entry;
3) in the common case when the protocol is file, bdrv_co_do_readv calls
bdrv_co_readv_em (and from here goes to bdrv_co_io_em), which yields
until the AIO operation is complete;
4) if bdrv_read had been called from a bottom half, the main loop
is free to iterate again: a device model or another bottom half
can then come and call bdrv_read again.
This applies to all four of read/write/flush/discard. It would also
apply to is_allocated, but it is not used from within coroutines:
besides qemu-img.c and qemu-io.c, which operate synchronously, the
only user is the monitor. Copy-on-read will introduce a use in the
block layer, and will require converting it.
The solution is "simply" to convert all drivers to coroutines! We
just need to add a CoMutex that is taken around affected operations.
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Diffstat (limited to 'qdict.c')
0 files changed, 0 insertions, 0 deletions