On 08/04/2017 10:14 AM, Vladimir Sementsov-Ogievskiy wrote: > Refactor nbd_read_eof to return 1 on success, 0 on eof, when no > data was read and <0 for other cases, because returned size of > read data is not actually used. > > Signed-off-by: Vladimir Sementsov-Ogievskiy <vsement...@virtuozzo.com> > --- > nbd/nbd-internal.h | 34 +++++++++++++++++++++++++--------- > nbd/client.c | 5 ----- > tests/qemu-iotests/083.out | 4 ++-- > 3 files changed, 27 insertions(+), 16 deletions(-) > > diff --git a/nbd/nbd-internal.h b/nbd/nbd-internal.h > index 396ddb4d3e..3fb0b6098a 100644 > --- a/nbd/nbd-internal.h > +++ b/nbd/nbd-internal.h > @@ -77,21 +77,37 @@ > #define NBD_ESHUTDOWN 108 > > /* nbd_read_eof > - * Tries to read @size bytes from @ioc. Returns number of bytes actually > read. > - * May return a value >= 0 and < size only on EOF, i.e. when iteratively > called > - * qio_channel_readv() returns 0. So, there is no need to call nbd_read_eof > - * iteratively. > + * Tries to read @size bytes from @ioc. > + * Returns 1 on success > + * 0 on eof, when no data was read (errp is not set) > + * -EINVAL on eof, when some data < @size was read until eof > + * < 0 on read fail
In general, mixing negative errno value and generic < 0 in the same
function is most likely ambiguous.
> */
> -static inline ssize_t nbd_read_eof(QIOChannel *ioc, void *buffer, size_t
> size,
> - Error **errp)
> +static inline int nbd_read_eof(QIOChannel *ioc, void *buffer, size_t size,
> + Error **errp)
> {
> struct iovec iov = { .iov_base = buffer, .iov_len = size };
> + ssize_t ret;
> +
> /* Sockets are kept in blocking mode in the negotiation phase. After
> * that, a non-readable socket simply means that another thread stole
> * our request/reply. Synchronization is done with recv_coroutine, so
> * that this is coroutine-safe.
> */
> - return nbd_rwv(ioc, &iov, 1, size, true, errp);
> +
> + assert(size > 0);
Effectively the same as assert(size != 0).
> +
> + ret = nbd_rwv(ioc, &iov, 1, size, true, errp);
> + if (ret <= 0) {
> + return ret;
> + }
So this is a negative errno (or 0 on EOF),
> +
> + if (ret != size) {
> + error_setg(errp, "End of file");
> + return -EINVAL;
and so is this. Which makes the function documentation not quite
accurate; you aren't mixing a generic < 0.
> + }
> +
> + return 1;
> }
>
> /* nbd_read
> @@ -100,9 +116,9 @@ static inline ssize_t nbd_read_eof(QIOChannel *ioc, void
> *buffer, size_t size,
> static inline int nbd_read(QIOChannel *ioc, void *buffer, size_t size,
> Error **errp)
> {
> - ssize_t ret = nbd_read_eof(ioc, buffer, size, errp);
> + int ret = nbd_read_eof(ioc, buffer, size, errp);
>
> - if (ret >= 0 && ret != size) {
> + if (ret == 0) {
> ret = -EINVAL;
> error_setg(errp, "End of file");
Why do we have to set errp here instead of in nbd_read_eof()? Is there
ever any case where hitting early EOF is not something that should be
treated as an error?
> }
> diff --git a/nbd/client.c b/nbd/client.c
> index f1c16b588f..4556056daa 100644
> --- a/nbd/client.c
> +++ b/nbd/client.c
> @@ -925,11 +925,6 @@ ssize_t nbd_receive_reply(QIOChannel *ioc, NBDReply
> *reply, Error **errp)
> return ret;
> }
>
> - if (ret != sizeof(buf)) {
> - error_setg(errp, "read failed");
> - return -EINVAL;
> - }
> -
> /* Reply
> [ 0 .. 3] magic (NBD_REPLY_MAGIC)
> [ 4 .. 7] error (0 == no error)
> diff --git a/tests/qemu-iotests/083.out b/tests/qemu-iotests/083.out
> index a24c6bfece..d3bea1b2f5 100644
> --- a/tests/qemu-iotests/083.out
> +++ b/tests/qemu-iotests/083.out
> @@ -69,12 +69,12 @@ read failed: Input/output error
>
> === Check disconnect 4 reply ===
>
> -read failed
> +End of file
> read failed: Input/output error
At least you tracked that your changes tweak the error message. But I'm
not yet convinced whether this change simplifies anything. Is there a
later patch that is easier to write with the new semantics which was not
possible with the pre-patch semantics?
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3266
Virtualization: qemu.org | libvirt.org
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