From 848c66e8f5b631961580f7f010a5831430dc84c2 Mon Sep 17 00:00:00 2001 From: Paolo Bonzini Date: Thu, 20 Oct 2011 13:16:21 +0200 Subject: 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 Signed-off-by: Kevin Wolf --- block/vpc.c | 2 ++ 1 file changed, 2 insertions(+) (limited to 'block/vpc.c') diff --git a/block/vpc.c b/block/vpc.c index cb6c570f44..9155ee15e3 100644 --- a/block/vpc.c +++ b/block/vpc.c @@ -110,6 +110,7 @@ struct vhd_dyndisk_header { }; typedef struct BDRVVPCState { + CoMutex lock; uint8_t footer_buf[HEADER_SIZE]; uint64_t free_data_block_offset; int max_table_entries; @@ -226,6 +227,7 @@ static int vpc_open(BlockDriverState *bs, int flags) s->last_pagetable = -1; #endif + qemu_co_mutex_init(&s->lock); return 0; fail: return err; -- cgit v1.2.1