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nbd: Don't inf-loop on early EOF 

Commit 7d3123e converted a single read_sync() into a while loop
that assumed that read_sync() would either make progress or give
an error. But when the server hangs up early, the client sees
EOF (a read_sync() of 0) and never makes progress, which in turn
caused qemu-iotest './check -nbd 83' to go into an infinite loop.

Rework the loop to accomodate reads cut short by EOF.

Reported-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <1478551093-32757-1-git-send-email-eblake@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Eric Blake 2016-11-07 14:38:13 -06:00 committed by Paolo Bonzini
parent 175cad36a5
commit a5068244b4
1 changed files with 7 additions and 6 deletions
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13
nbd/client.c
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@ -90,20 +90,21 @@ static QTAILQ_HEAD(, NBDExport) exports = QTAILQ_HEAD_INITIALIZER(exports);
* the amount of bytes consumed. */
static ssize_t drop_sync(QIOChannel *ioc, size_t size)
{
ssize_t ret, dropped = size;
ssize_t ret = 0;
char small[1024];
char *buffer;
buffer = sizeof(small) < size ? small : g_malloc(MIN(65536, size));
while (size > 0) {
ret = read_sync(ioc, buffer, MIN(65536, size));
if (ret < 0) {
ssize_t count = read_sync(ioc, buffer, MIN(65536, size));
if (count <= 0) {
goto cleanup;
}
assert(ret <= size);
size -= ret;
assert(count <= size);
size -= count;
ret += count;
}
ret = dropped;
cleanup:
if (buffer != small) {