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nbd: Use low-level QIOChannel API in nbd_read_eof()

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Instead of using the convenience wrapper qio_channel_read_all_eof(), use
the lower level QIOChannel API. This means duplicating some code, but
we'll need this because this coroutine yield is special: We want it to
be interruptible so that nbd_client_attach_aio_context() can correctly
reenter the coroutine.

This moves the bdrv_dec/inc_in_flight() pair into nbd_read_eof(), so
that connection_co will always sit in this exact qio_channel_yield()
call when bdrv_drain() returns.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
This commit is contained in:
Kevin Wolf 2019-02-18 14:56:01 +01:00
parent a7b78fc944
commit d3bd5b9089
3 changed files with 40 additions and 18 deletions
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8
block/nbd-client.c
View File

@ -84,15 +84,9 @@ static coroutine_fn void nbd_connection_entry(void *opaque)
*
* Therefore we keep an additional in_flight reference all the time and
* only drop it temporarily here.
*
* FIXME This is not safe because the QIOChannel could wake up the
* coroutine for a second time; it is not prepared for coroutine
* resumption from external code.
*/
bdrv_dec_in_flight(s->bs);
assert(s->reply.handle == 0);
ret = nbd_receive_reply(s->ioc, &s->reply, &local_err);
bdrv_inc_in_flight(s->bs);
ret = nbd_receive_reply(s->bs, s->ioc, &s->reply, &local_err);
if (local_err) {
trace_nbd_read_reply_entry_fail(ret, error_get_pretty(local_err));

4
include/block/nbd.h
View File

@ -300,8 +300,8 @@ int nbd_receive_export_list(QIOChannel *ioc, QCryptoTLSCreds *tlscreds,
int nbd_init(int fd, QIOChannelSocket *sioc, NBDExportInfo *info,
Error **errp);
int nbd_send_request(QIOChannel *ioc, NBDRequest *request);
int coroutine_fn nbd_receive_reply(QIOChannel *ioc, NBDReply *reply,
Error **errp);
int coroutine_fn nbd_receive_reply(BlockDriverState *bs, QIOChannel *ioc,
NBDReply *reply, Error **errp);
int nbd_client(int fd);
int nbd_disconnect(int fd);
int nbd_errno_to_system_errno(int err);

46
nbd/client.c
View File

@ -1394,30 +1394,58 @@ static int nbd_receive_structured_reply_chunk(QIOChannel *ioc,
* negative errno on failure (errp is set)
*/
static inline int coroutine_fn
nbd_read_eof(QIOChannel *ioc, void *buffer, size_t size, Error **errp)
nbd_read_eof(BlockDriverState *bs, QIOChannel *ioc, void *buffer, size_t size,
Error **errp)
{
int ret;
bool partial = false;
assert(size);
ret = qio_channel_read_all_eof(ioc, buffer, size, errp);
if (ret < 0) {
ret = -EIO;
while (size > 0) {
struct iovec iov = { .iov_base = buffer, .iov_len = size };
ssize_t len;
len = qio_channel_readv(ioc, &iov, 1, errp);
if (len == QIO_CHANNEL_ERR_BLOCK) {
bdrv_dec_in_flight(bs);
qio_channel_yield(ioc, G_IO_IN);
bdrv_inc_in_flight(bs);
continue;
} else if (len < 0) {
return -EIO;
} else if (len == 0) {
if (partial) {
error_setg(errp,
"Unexpected end-of-file before all bytes were read");
return -EIO;
} else {
return 0;
}
return ret;
}
partial = true;
size -= len;
buffer = (uint8_t*) buffer + len;
}
return 1;
}
/* nbd_receive_reply
*
* Decreases bs->in_flight while waiting for a new reply. This yield is where
* we wait indefinitely and the coroutine must be able to be safely reentered
* for nbd_client_attach_aio_context().
*
* Returns 1 on success
* 0 on eof, when no data was read (errp is not set)
* negative errno on failure (errp is set)
*/
int coroutine_fn nbd_receive_reply(QIOChannel *ioc, NBDReply *reply,
Error **errp)
int coroutine_fn nbd_receive_reply(BlockDriverState *bs, QIOChannel *ioc,
NBDReply *reply, Error **errp)
{
int ret;
const char *type;
ret = nbd_read_eof(ioc, &reply->magic, sizeof(reply->magic), errp);
ret = nbd_read_eof(bs, ioc, &reply->magic, sizeof(reply->magic), errp);
if (ret <= 0) {
return ret;
}