/qemu/nbd/ |
H A D | common.c | dacca04c Thu Apr 07 11:25:08 GMT 2016 Paolo Bonzini <pbonzini@redhat.com> nbd: do not hang nbd_wr_syncv if outside a coroutine and no available data
Until commit 1c778ef7 ("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 commit 1c778ef7.
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> dacca04c Thu Apr 07 11:25:08 GMT 2016 Paolo Bonzini <pbonzini@redhat.com> nbd: do not hang nbd_wr_syncv if outside a coroutine and no available data
Until commit 1c778ef7 ("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 commit 1c778ef7.
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> 1c778ef7 Wed Feb 10 18:41:04 GMT 2016 Daniel P. Berrange <berrange@redhat.com> nbd: convert to using I/O channels for actual socket I/O
Now that all callers are converted to use I/O channels for initial connection setup, it is possible to switch the core NBD protocol handling core over to use QIOChannel APIs for actual sockets I/O.
Signed-off-by: Daniel P. Berrange <berrange@redhat.com> Message-Id: <1455129674-17255-7-git-send-email-berrange@redhat.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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H A D | nbd-internal.h | 1c778ef7 Wed Feb 10 18:41:04 GMT 2016 Daniel P. Berrange <berrange@redhat.com> nbd: convert to using I/O channels for actual socket I/O
Now that all callers are converted to use I/O channels for initial connection setup, it is possible to switch the core NBD protocol handling core over to use QIOChannel APIs for actual sockets I/O.
Signed-off-by: Daniel P. Berrange <berrange@redhat.com> Message-Id: <1455129674-17255-7-git-send-email-berrange@redhat.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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H A D | client.c | 1c778ef7 Wed Feb 10 18:41:04 GMT 2016 Daniel P. Berrange <berrange@redhat.com> nbd: convert to using I/O channels for actual socket I/O
Now that all callers are converted to use I/O channels for initial connection setup, it is possible to switch the core NBD protocol handling core over to use QIOChannel APIs for actual sockets I/O.
Signed-off-by: Daniel P. Berrange <berrange@redhat.com> Message-Id: <1455129674-17255-7-git-send-email-berrange@redhat.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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H A D | server.c | 1c778ef7 Wed Feb 10 18:41:04 GMT 2016 Daniel P. Berrange <berrange@redhat.com> nbd: convert to using I/O channels for actual socket I/O
Now that all callers are converted to use I/O channels for initial connection setup, it is possible to switch the core NBD protocol handling core over to use QIOChannel APIs for actual sockets I/O.
Signed-off-by: Daniel P. Berrange <berrange@redhat.com> Message-Id: <1455129674-17255-7-git-send-email-berrange@redhat.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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/qemu/ |
H A D | blockdev-nbd.c | 1c778ef7 Wed Feb 10 18:41:04 GMT 2016 Daniel P. Berrange <berrange@redhat.com> nbd: convert to using I/O channels for actual socket I/O
Now that all callers are converted to use I/O channels for initial connection setup, it is possible to switch the core NBD protocol handling core over to use QIOChannel APIs for actual sockets I/O.
Signed-off-by: Daniel P. Berrange <berrange@redhat.com> Message-Id: <1455129674-17255-7-git-send-email-berrange@redhat.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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H A D | qemu-nbd.c | 1c778ef7 Wed Feb 10 18:41:04 GMT 2016 Daniel P. Berrange <berrange@redhat.com> nbd: convert to using I/O channels for actual socket I/O
Now that all callers are converted to use I/O channels for initial connection setup, it is possible to switch the core NBD protocol handling core over to use QIOChannel APIs for actual sockets I/O.
Signed-off-by: Daniel P. Berrange <berrange@redhat.com> Message-Id: <1455129674-17255-7-git-send-email-berrange@redhat.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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/qemu/include/block/ |
H A D | nbd.h | 1c778ef7 Wed Feb 10 18:41:04 GMT 2016 Daniel P. Berrange <berrange@redhat.com> nbd: convert to using I/O channels for actual socket I/O
Now that all callers are converted to use I/O channels for initial connection setup, it is possible to switch the core NBD protocol handling core over to use QIOChannel APIs for actual sockets I/O.
Signed-off-by: Daniel P. Berrange <berrange@redhat.com> Message-Id: <1455129674-17255-7-git-send-email-berrange@redhat.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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