dacca04c8d
Until commit1c778ef7("nbd: convert to using I/O channels for actual socket I/O", 2016-02-16), nbd_wr_sync returned -EAGAIN this scenario. nbd_reply_ready required these semantics because it has two conflicting requirements: 1) if a reply can be received on the socket, nbd_reply_ready needs to read the header outside coroutine context to identify _which_ coroutine to enter to process the rest of the reply 2) on the other hand, nbd_reply_ready can find a false positive if another thread (e.g. a VCPU thread running aio_poll) sneaks in and calls nbd_reply_ready too. In this case nbd_reply_ready does nothing and expects nbd_wr_syncv to return -EAGAIN. Currently, the solution to the first requirement is to wait in the very rare case of a read() that doesn't retrieve the reply header in its entirety; this is what nbd_wr_syncv does by calling qio_channel_wait(). However, the unconditional call to qio_channel_wait() breaks the second requirement. To fix this, the patch makes nbd_wr_syncv return -EAGAIN if done is zero, similar to the code before commit1c778ef7. This is okay because NBD client-side negotiation is the only other case that calls nbd_wr_syncv outside a coroutine, and it places the socket in blocking mode. On the other hand, it is a bit unpleasant to put this in nbd_wr_syncv(), because the function is used by both client and server. The full fix would be to add a counter to NbdClientSession for how many bytes have been filled in s->reply. Then a reply can be filled by multiple separate invocations of nbd_reply_ready and the qio_channel_wait() call can be removed completely. Something to consider for 2.7... Reported-by: Changlong Xie <xiecl.fnst@cn.fujitsu.com> Reviewed-by: Daniel P. Berrange <berrange@redhat.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
97 lines
2.9 KiB
C
97 lines
2.9 KiB
C
/*
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* Copyright (C) 2005 Anthony Liguori <anthony@codemonkey.ws>
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*
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* Network Block Device Common Code
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; under version 2 of the License.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, see <http://www.gnu.org/licenses/>.
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*/
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#include "qemu/osdep.h"
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#include "qapi/error.h"
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#include "nbd-internal.h"
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ssize_t nbd_wr_syncv(QIOChannel *ioc,
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struct iovec *iov,
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size_t niov,
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size_t offset,
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size_t length,
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bool do_read)
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{
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ssize_t done = 0;
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Error *local_err = NULL;
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struct iovec *local_iov = g_new(struct iovec, niov);
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struct iovec *local_iov_head = local_iov;
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unsigned int nlocal_iov = niov;
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nlocal_iov = iov_copy(local_iov, nlocal_iov,
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iov, niov,
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offset, length);
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while (nlocal_iov > 0) {
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ssize_t len;
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if (do_read) {
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len = qio_channel_readv(ioc, local_iov, nlocal_iov, &local_err);
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} else {
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len = qio_channel_writev(ioc, local_iov, nlocal_iov, &local_err);
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}
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if (len == QIO_CHANNEL_ERR_BLOCK) {
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if (qemu_in_coroutine()) {
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/* XXX figure out if we can create a variant on
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* qio_channel_yield() that works with AIO contexts
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* and consider using that in this branch */
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qemu_coroutine_yield();
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} else if (done) {
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/* XXX this is needed by nbd_reply_ready. */
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qio_channel_wait(ioc,
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do_read ? G_IO_IN : G_IO_OUT);
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} else {
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return -EAGAIN;
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}
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continue;
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}
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if (len < 0) {
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TRACE("I/O error: %s", error_get_pretty(local_err));
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error_free(local_err);
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/* XXX handle Error objects */
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done = -EIO;
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goto cleanup;
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}
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if (do_read && len == 0) {
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break;
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}
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iov_discard_front(&local_iov, &nlocal_iov, len);
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done += len;
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}
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cleanup:
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g_free(local_iov_head);
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return done;
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}
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void nbd_tls_handshake(Object *src,
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Error *err,
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void *opaque)
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{
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struct NBDTLSHandshakeData *data = opaque;
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if (err) {
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TRACE("TLS failed %s", error_get_pretty(err));
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data->error = error_copy(err);
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}
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data->complete = true;
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g_main_loop_quit(data->loop);
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}
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