block/curl: Handle failed reads gracefully.
Current behaviour if a read fails is for the acb to not get finished. This causes an infinite loop in bdrv_read_em (block.c). The read failure never gets reported to the guest and if the error condition clears, the process never recovers. With this patch, when curl reports a failure we finish the acb as a failure. This results in the guest receiving an I/O error (rather than the read hanging indefinitely) and if the error condition subsequently clears, retries work as expected. The simplest test is to put an ISO on a web server you have control over and open it with qemu-io. Then move the ISO out of the way and attempt to read some data - you should see behaviour matching the above. Signed-off-by: NNick Thomas <nick@bytemark.co.uk> Signed-off-by: NKevin Wolf <kwolf@redhat.com>
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