Re: [Qemu-devel] [PATCH for-2.8] nbd: Don't inf-loop on early EOF

[Eric Blake <eblake@redhat.com>]

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[updating subject line, to make sure this regression is fixed]

On 11/07/2016 02:38 PM, Eric Blake wrote:
> 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.

and s/accomodate/accommodate/ if the maintainer would be so nice (not
every day I get to correct my own typos)

> 
> Reported-by: Max Reitz <mreitz@redhat.com>
> Signed-off-by: Eric Blake <eblake@redhat.com>
> ---
>  nbd/client.c | 13 +++++++------
>  1 file changed, 7 insertions(+), 6 deletions(-)
> 
> diff --git a/nbd/client.c b/nbd/client.c
> index 5d94e34..29b6edf 100644
> --- a/nbd/client.c
> +++ b/nbd/client.c
> @@ -79,20 +79,21 @@ 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) {
> 

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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