Re: [PATCH for-9.1 v2 04/11] vhost-user-server: don't abort if we can't set fd non-blocking
On Tue, Mar 26, 2024 at 09:40:12AM -0500, Eric Blake wrote:
On Tue, Mar 26, 2024 at 02:39:29PM +0100, Stefano Garzarella wrote:
In vhost-user-server we set all fd received from the other peer
in non-blocking mode. For some of them (e.g. memfd, shm_open, etc.)
if we fail, it's not really a problem, because we don't use these
fd with blocking operations, but only to map memory.
In these cases a failure is not bad, so let's just report a warning
instead of panicking if we fail to set some fd in non-blocking mode.
This for example occurs in macOS where setting shm_open() fd
non-blocking is failing (errno: 25).
What is errno 25 on MacOS?
It should be ENOTTY.
I'll add in the commit description.
Signed-off-by: Stefano Garzarella
---
util/vhost-user-server.c | 6 +-
1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/util/vhost-user-server.c b/util/vhost-user-server.c
index 3bfb1ad3ec..064999f0b7 100644
--- a/util/vhost-user-server.c
+++ b/util/vhost-user-server.c
@@ -66,7 +66,11 @@ static void vmsg_unblock_fds(VhostUserMsg *vmsg)
{
int i;
for (i = 0; i < vmsg->fd_num; i++) {
-qemu_socket_set_nonblock(vmsg->fds[i]);
+int ret = qemu_socket_try_set_nonblock(vmsg->fds[i]);
+if (ret) {
Should this be 'if (ret < 0)'?
I was confused by the assert() in qemu_socket_set_nonblock():
void qemu_socket_set_nonblock(int fd)
{
int f;
f = qemu_socket_try_set_nonblock(fd);
assert(f == 0);
}
BTW, I see most of the code checks ret < 0, so I'll fix it.
+warn_report("Failed to set fd %d nonblock for request %d: %s",
+vmsg->fds[i], vmsg->request, strerror(-ret));
+}
This now ignores all errors even on pre-existing fds where we NEED
non-blocking, rather than just the specific (expected) error we are
seeing on MacOS. Should this code be a bit more precise about
checking that -ret == EXXX for the expected errno value we are
ignoring for the specific fds where non-blocking is not essential?
Good point, maybe I'll just avoid calling vmsg_unblock_fds() when the
message is VHOST_USER_ADD_MEM_REG or VHOST_USER_SET_MEM_TABLE.
These should be the cases where carried fds are used for mmap() and so
there is no need to mark them non-blocking.
WDYT?
Stefano
Re: [PATCH for-9.1 v2 04/11] vhost-user-server: don't abort if we can't set fd non-blocking
On Tue, Mar 26, 2024 at 02:39:29PM +0100, Stefano Garzarella wrote:
> In vhost-user-server we set all fd received from the other peer
> in non-blocking mode. For some of them (e.g. memfd, shm_open, etc.)
> if we fail, it's not really a problem, because we don't use these
> fd with blocking operations, but only to map memory.
>
> In these cases a failure is not bad, so let's just report a warning
> instead of panicking if we fail to set some fd in non-blocking mode.
>
> This for example occurs in macOS where setting shm_open() fd
> non-blocking is failing (errno: 25).
What is errno 25 on MacOS?
>
> Signed-off-by: Stefano Garzarella
> ---
> util/vhost-user-server.c | 6 +-
> 1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/util/vhost-user-server.c b/util/vhost-user-server.c
> index 3bfb1ad3ec..064999f0b7 100644
> --- a/util/vhost-user-server.c
> +++ b/util/vhost-user-server.c
> @@ -66,7 +66,11 @@ static void vmsg_unblock_fds(VhostUserMsg *vmsg)
> {
> int i;
> for (i = 0; i < vmsg->fd_num; i++) {
> -qemu_socket_set_nonblock(vmsg->fds[i]);
> +int ret = qemu_socket_try_set_nonblock(vmsg->fds[i]);
> +if (ret) {
Should this be 'if (ret < 0)'?
> +warn_report("Failed to set fd %d nonblock for request %d: %s",
> +vmsg->fds[i], vmsg->request, strerror(-ret));
> +}
This now ignores all errors even on pre-existing fds where we NEED
non-blocking, rather than just the specific (expected) error we are
seeing on MacOS. Should this code be a bit more precise about
checking that -ret == EXXX for the expected errno value we are
ignoring for the specific fds where non-blocking is not essential?
--
Eric Blake, Principal Software Engineer
Red Hat, Inc.
Virtualization: qemu.org | libguestfs.org
[PATCH for-9.1 v2 04/11] vhost-user-server: don't abort if we can't set fd non-blocking
In vhost-user-server we set all fd received from the other peer
in non-blocking mode. For some of them (e.g. memfd, shm_open, etc.)
if we fail, it's not really a problem, because we don't use these
fd with blocking operations, but only to map memory.
In these cases a failure is not bad, so let's just report a warning
instead of panicking if we fail to set some fd in non-blocking mode.
This for example occurs in macOS where setting shm_open() fd
non-blocking is failing (errno: 25).
Signed-off-by: Stefano Garzarella
---
util/vhost-user-server.c | 6 +-
1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/util/vhost-user-server.c b/util/vhost-user-server.c
index 3bfb1ad3ec..064999f0b7 100644
--- a/util/vhost-user-server.c
+++ b/util/vhost-user-server.c
@@ -66,7 +66,11 @@ static void vmsg_unblock_fds(VhostUserMsg *vmsg)
{
int i;
for (i = 0; i < vmsg->fd_num; i++) {
-qemu_socket_set_nonblock(vmsg->fds[i]);
+int ret = qemu_socket_try_set_nonblock(vmsg->fds[i]);
+if (ret) {
+warn_report("Failed to set fd %d nonblock for request %d: %s",
+vmsg->fds[i], vmsg->request, strerror(-ret));
+}
}
}
--
2.44.0
