[libvirt PATCH] rpc: don't try to spawn non-existant daemon

[Martin Kletzander]

On Wed, Jan 25, 2023 at 04:06:49PM +0100, Martin Kletzander wrote:
>On Wed, Jan 25, 2023 at 02:27:09PM +0000, Daniel P. Berrangé wrote:
>>If libvirt is built in client only mode, the libvirtd/virtqemud/etc
>>daemons won't exist. If the client is told to connect to a local
>>hypervisor, it'll see the socket doesn't exist, try to spawn the
>>daemon and then re-try connecting to the socket for a few seconds.
>>Ultimately this will fail because the daemon doesn't exist and the
>>user gets an error message
>>
>>  error: Failed to connect socket to '/run/user/1000/libvirt/virtqemud-sock': No such file or directory
>>
>>technically this is accurate, but it doesn't help identify the root
>>cause. With this change it will now report
>>
>>  error: binary 'virtqemud' does not exist in $PATH: No such file or directory
>>
>>and will skip all the socket connect retries
>>

Actually, Michal had a good question, this should fail in virCommandRun,
and looking at virExec it even does the virFindFileInPath if the first
argument is not absolute and errors out if the path cannot be found.
You might still get ENOENT when running the binary in case a linked
library is missing or something and even without this check.  I guess
our double-fork() in virExec() might be at fault?  When not using a
pidfile there is no wait for the second child to let us know that it
failed (or close the pipesync[1]).  Maybe that is the root cause?

>>Signed-off-by: Daniel P. Berrangé <berrange at redhat.com>
>
>Reviewed-by: Martin Kletzander <mkletzan at redhat.com>
>
>>---
>> src/rpc/virnetsocket.c | 16 +++++++++++++---
>> 1 file changed, 13 insertions(+), 3 deletions(-)
>>
>>diff --git a/src/rpc/virnetsocket.c b/src/rpc/virnetsocket.c
>>index 8280bda007..bb2e0c5d3d 100644
>>--- a/src/rpc/virnetsocket.c
>>+++ b/src/rpc/virnetsocket.c
>>@@ -123,9 +123,19 @@ VIR_ONCE_GLOBAL_INIT(virNetSocket);
>> #ifndef WIN32
>> static int virNetSocketForkDaemon(const char *binary)
>> {
>>-    g_autoptr(virCommand) cmd = virCommandNewArgList(binary,
>>-                                                     "--timeout=120",
>>-                                                     NULL);
>>+    g_autofree char *binarypath = virFindFileInPath(binary);
>>+    g_autoptr(virCommand) cmd = NULL;
>>+
>>+    if (!binarypath) {
>>+        virReportSystemError(ENOENT,
>>+                             _("binary '%s' does not exist in $PATH"),
>>+                             binary);
>>+        return -1;
>>+    }
>>+
>>+    cmd = virCommandNewArgList(binarypath,
>>+                               "--timeout=120",
>>+                               NULL);
>>
>>     virCommandAddEnvPassCommon(cmd);
>>     virCommandAddEnvPass(cmd, "XDG_CACHE_HOME");
>>--
>>2.39.0
>>


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