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Re: [Qemu-devel] [PATCH v2 4/4] 9pfs: handle broken transport
From: |
Stefano Stabellini |
Subject: |
Re: [Qemu-devel] [PATCH v2 4/4] 9pfs: handle broken transport |
Date: |
Thu, 27 Apr 2017 11:51:24 -0700 (PDT) |
User-agent: |
Alpine 2.10 (DEB 1266 2009-07-14) |
On Thu, 27 Apr 2017, Greg Kurz wrote:
> The 9p protocol is transport agnostic: if an error occurs when copying data
> to/from the client, this should be handled by the transport layer [1] and
> the 9p server should simply stop processing requests [2].
>
> [1] can be implemented in the transport marshal/unmarshal handlers. In the
> case of virtio, this means calling virtio_error() to inform the guest that
> the device isn't functional anymore.
>
> [2] means that the pdu_complete() function shouldn't send a reply back to
> the client if the transport had a failure. This cannot be decided using the
> current error path though, since we cannot discriminate if the error comes
> from the transport or the backend. This patch hence introduces a flag in
> the 9pfs state to record that the transport is broken. The device needs to
> be reset for the flag to be unset.
>
> This fixes Coverity issue CID 1348518.
>
> Signed-off-by: Greg Kurz <address@hidden>
> ---
> v2: - use unlikely() when checking if the transport is broken
> - fail marshal/unmarshal if transport is broken
> - v9fs_xattr_read() mark transport as broken if v9fs_pack() fails
> ---
> hw/9pfs/9p.c | 45
> ++++++++++++++++++++++++++++++++++++--------
> hw/9pfs/9p.h | 1 +
> hw/9pfs/virtio-9p-device.c | 16 ++++++++++++++--
> 3 files changed, 52 insertions(+), 10 deletions(-)
>
> diff --git a/hw/9pfs/9p.c b/hw/9pfs/9p.c
> index 01deffa0c3b5..406c1937ed21 100644
> --- a/hw/9pfs/9p.c
> +++ b/hw/9pfs/9p.c
> @@ -46,10 +46,17 @@ ssize_t pdu_marshal(V9fsPDU *pdu, size_t offset, const
> char *fmt, ...)
> ssize_t ret;
> va_list ap;
>
> + if (unlikely(pdu->s->transport_broken)) {
> + return -EIO;
> + }
> +
> va_start(ap, fmt);
> ret = pdu->s->transport->pdu_vmarshal(pdu, offset, fmt, ap);
> va_end(ap);
>
> + if (ret < 0) {
> + pdu->s->transport_broken = true;
> + }
> return ret;
> }
>
> @@ -58,10 +65,17 @@ ssize_t pdu_unmarshal(V9fsPDU *pdu, size_t offset, const
> char *fmt, ...)
> ssize_t ret;
> va_list ap;
>
> + if (unlikely(pdu->s->transport_broken)) {
> + return -EIO;
> + }
> +
> va_start(ap, fmt);
> ret = pdu->s->transport->pdu_vunmarshal(pdu, offset, fmt, ap);
> va_end(ap);
>
> + if (ret < 0) {
> + pdu->s->transport_broken = true;
> + }
> return ret;
> }
>
> @@ -624,15 +638,15 @@ void pdu_free(V9fsPDU *pdu)
> QLIST_INSERT_HEAD(&s->free_list, pdu, next);
> }
>
> -/*
> - * We don't do error checking for pdu_marshal/unmarshal here
> - * because we always expect to have enough space to encode
> - * error details
> - */
> static void coroutine_fn pdu_complete(V9fsPDU *pdu, ssize_t len)
> {
> int8_t id = pdu->id + 1; /* Response */
> V9fsState *s = pdu->s;
> + int ret;
> +
> + if (unlikely(s->transport_broken)) {
> + goto out_complete;
> + }
>
> if (len < 0) {
> int err = -len;
> @@ -644,11 +658,19 @@ static void coroutine_fn pdu_complete(V9fsPDU *pdu,
> ssize_t len)
> str.data = strerror(err);
> str.size = strlen(str.data);
>
> - len += pdu_marshal(pdu, len, "s", &str);
> + ret = pdu_marshal(pdu, len, "s", &str);
> + if (ret < 0) {
> + goto out_complete;
> + }
> + len += ret;
> id = P9_RERROR;
> }
>
> - len += pdu_marshal(pdu, len, "d", err);
> + ret = pdu_marshal(pdu, len, "d", err);
> + if (ret < 0) {
> + goto out_complete;
> + }
> + len += ret;
>
> if (s->proto_version == V9FS_PROTO_2000L) {
> id = P9_RLERROR;
> @@ -657,7 +679,10 @@ static void coroutine_fn pdu_complete(V9fsPDU *pdu,
> ssize_t len)
> }
>
> /* fill out the header */
> - pdu_marshal(pdu, 0, "dbw", (int32_t)len, id, pdu->tag);
> + ret = pdu_marshal(pdu, 0, "dbw", (int32_t)len, id, pdu->tag);
> + if (ret < 0) {
> + goto out_complete;
> + }
If I am not mistaken, none of these "if (ret < 0)" are necessary in
pdu_complete. Just like any of the other call sites of
pdu_marshal/pdu_unmarshal, we could just let it go through the calls,
which would actually do nothing once transport_broken is set.
We could move the transport_broken check right before the call to
push_and_notify.
> /* keep these in sync */
> pdu->size = len;
> @@ -665,6 +690,7 @@ static void coroutine_fn pdu_complete(V9fsPDU *pdu,
> ssize_t len)
>
> pdu->s->transport->push_and_notify(pdu);
>
> +out_complete:
> /* Now wakeup anybody waiting in flush for this request */
> if (!qemu_co_queue_next(&pdu->complete)) {
> pdu_free(pdu);
> @@ -1702,6 +1728,7 @@ static int v9fs_xattr_read(V9fsState *s, V9fsPDU *pdu,
> V9fsFidState *fidp,
> read_count);
> qemu_iovec_destroy(&qiov_full);
> if (err < 0) {
> + s->transport_broken = true;
> return err;
> }
> offset += err;
> @@ -3596,6 +3623,8 @@ void v9fs_reset(V9fsState *s)
> while (!data.done) {
> aio_poll(qemu_get_aio_context(), true);
> }
> +
> + s->transport_broken = false;
> }
>
> static void __attribute__((__constructor__)) v9fs_set_fd_limit(void)
> diff --git a/hw/9pfs/9p.h b/hw/9pfs/9p.h
> index 5312d8a42405..145d0c87dd6a 100644
> --- a/hw/9pfs/9p.h
> +++ b/hw/9pfs/9p.h
> @@ -246,6 +246,7 @@ typedef struct V9fsState
> Error *migration_blocker;
> V9fsConf fsconf;
> V9fsQID root_qid;
> + bool transport_broken;
> } V9fsState;
>
> /* 9p2000.L open flags */
> diff --git a/hw/9pfs/virtio-9p-device.c b/hw/9pfs/virtio-9p-device.c
> index c71659823fdc..9e61fbf7c63e 100644
> --- a/hw/9pfs/virtio-9p-device.c
> +++ b/hw/9pfs/virtio-9p-device.c
> @@ -158,8 +158,14 @@ static ssize_t virtio_pdu_vmarshal(V9fsPDU *pdu, size_t
> offset,
> V9fsState *s = pdu->s;
> V9fsVirtioState *v = container_of(s, V9fsVirtioState, state);
> VirtQueueElement *elem = v->elems[pdu->idx];
> + int ret;
>
> - return v9fs_iov_vmarshal(elem->in_sg, elem->in_num, offset, 1, fmt, ap);
> + ret = v9fs_iov_vmarshal(elem->in_sg, elem->in_num, offset, 1, fmt, ap);
> + if (ret < 0) {
> + virtio_9p_error(v, pdu->idx,
> + "Failed to marshal VirtFS reply type %d", pdu->id);
> + }
> + return ret;
> }
>
> static ssize_t virtio_pdu_vunmarshal(V9fsPDU *pdu, size_t offset,
> @@ -168,8 +174,14 @@ static ssize_t virtio_pdu_vunmarshal(V9fsPDU *pdu,
> size_t offset,
> V9fsState *s = pdu->s;
> V9fsVirtioState *v = container_of(s, V9fsVirtioState, state);
> VirtQueueElement *elem = v->elems[pdu->idx];
> + int ret;
>
> - return v9fs_iov_vunmarshal(elem->out_sg, elem->out_num, offset, 1, fmt,
> ap);
> + ret = v9fs_iov_vunmarshal(elem->out_sg, elem->out_num, offset, 1, fmt,
> ap);
> + if (ret < 0) {
> + virtio_9p_error(v, pdu->idx,
> + "Failed to unmarshal VirtFS request type %d",
> pdu->id);
> + }
> + return ret;
> }
>
> /* The size parameter is used by other transports. Do not drop it. */
- [Qemu-devel] [PATCH v2 0/4] 9pfs: handle transport errors, Greg Kurz, 2017/04/27
- [Qemu-devel] [PATCH v2 1/4] fsdev: don't allow unknown format in marshal/unmarshal, Greg Kurz, 2017/04/27
- [Qemu-devel] [PATCH v2 2/4] 9pfs: drop pdu_push_and_notify(), Greg Kurz, 2017/04/27
- [Qemu-devel] [PATCH v2 3/4] virtio-9p: factor out virtio_9p_error_err(), Greg Kurz, 2017/04/27
- [Qemu-devel] [PATCH v2 4/4] 9pfs: handle broken transport, Greg Kurz, 2017/04/27
- Re: [Qemu-devel] [PATCH v2 4/4] 9pfs: handle broken transport,
Stefano Stabellini <=
- Re: [Qemu-devel] [PATCH v2 0/4] 9pfs: handle transport errors, no-reply, 2017/04/27