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Only await POLLOUT events until connected

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Non-blocking socket connect(2) involves waiting for the socket to become
writeable to detect that a connection has been made.  POLLIN events
should not be requested until the socket is connected because they are
processed even if the iSCSI context is not yet connected.

For example, the QEMU iscsi block driver does something like this:

iscsi_full_connect_async(...)

/* Now wait until the socket becomes ready */
poll(POLLIN|POLLOUT) = POLLIN|POLLOUT

/* QEMU calls POLLIN and POLLOUT handlers individually and it happens to
 * call the POLLIN handler *before* the POLLOUT handler.
 */
iscsi_service(POLLIN)
iscsi_service(POLLOUT)

POLLIN processing will read from the socket and consume the error code
if connect failed.  As a result, the POLLOUT handler will write to a
disconnected socket and raise a SIGPIPE which kills the process.

Signed-off-by: Stefan Hajnoczi <stefanha@gmail.com>
This commit is contained in:
Stefan Hajnoczi
2010-12-29 08:40:09 +00:00
parent f449b31150
commit faec3c0dfd
1 changed files with 1 additions and 5 deletions
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6
lib/socket.c
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@@ -165,11 +165,7 @@ iscsi_get_fd(struct iscsi_context *iscsi)
int
iscsi_which_events(struct iscsi_context *iscsi)
{
int events = POLLIN;
if (iscsi->is_connected == 0) {
events |= POLLOUT;
}
int events = iscsi->is_connected ? POLLIN : POLLOUT;
if (iscsi->outqueue) {
events |= POLLOUT;