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sockets: allow SocketAddress 'fd' to reference numeric file descriptors

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The SocketAddress 'fd' kind accepts the name of a file descriptor passed
to the monitor with the 'getfd' command. This makes it impossible to use
the 'fd' kind in cases where a monitor is not available. This can apply in
handling command line argv at startup, or simply if internal code wants to
use SocketAddress and pass a numeric FD it has acquired from elsewhere.

Fortunately the 'getfd' command mandated that the FD names must not start
with a leading digit. We can thus safely extend semantics of the
SocketAddress 'fd' kind, to allow a purely numeric name to reference an
file descriptor that QEMU already has open. There will be restrictions on
when each kind can be used.

In codepaths where we are handling a monitor command (ie cur_mon != NULL),
we will only support use of named file descriptors as before. Use of FD
numbers is still not permitted for monitor commands.

In codepaths where we are not handling a monitor command (ie cur_mon ==
NULL), we will not support named file descriptors. Instead we can reference
FD numers explicitly. This allows the app spawning QEMU to intentionally
"leak" a pre-opened socket to QEMU and reference that in a SocketAddress
definition, or for code inside QEMU to pass pre-opened FDs around.

Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
This commit is contained in:
Daniel P. Berrange 2017-12-22 11:04:30 +00:00 • committed by Daniel P. Berrangé
parent 30bdb3c56d
commit 1723d6b1cf
3 changed files with 126 additions and 9 deletions
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16
util/qemu-sockets.c
View file

@ -1044,9 +1044,19 @@ fail:
static int socket_get_fd(const char *fdstr, Error **errp)
{
int fd = monitor_get_fd(cur_mon, fdstr, errp);
if (fd < 0) {
return -1;
int fd;
if (cur_mon) {
fd = monitor_get_fd(cur_mon, fdstr, errp);
if (fd < 0) {
return -1;
}
} else {
if (qemu_strtoi(fdstr, NULL, 10, &fd) < 0) {
error_setg_errno(errp, errno,
"Unable to parse FD number %s",
fdstr);
return -1;
}
}
if (!fd_is_socket(fd)) {
error_setg(errp, "File descriptor '%s' is not a socket", fdstr);