From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Fiona Ebner <f.ebner@proxmox.com>
Date: Mon, 18 Dec 2023 11:13:40 +0100
Subject: [PATCH] qemu_init: increase NOFILE soft limit on POSIX
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In many configurations, e.g. multiple vNICs with multiple queues or
with many Ceph OSDs, the default soft limit of 1024 is not enough.
QEMU is supposed to work fine with file descriptors >= 1024 and does
not use select() on POSIX. Bump the soft limit to the allowed hard
limit to avoid issues with the aforementioned configurations.

Of course the limit could be raised from the outside, but the man page
of systemd.exec states about 'LimitNOFILE=':

> Don't use.
> [...]
> Typically applications should increase their soft limit to the hard
> limit on their own, if they are OK with working with file
> descriptors above 1023,

If the soft limit is already the same as the hard limit, avoid the
superfluous setrlimit call. This can avoid a warning with a strict
seccomp filter blocking setrlimit if NOFILE was already raised before
executing QEMU.

Buglink: https://bugzilla.proxmox.com/show_bug.cgi?id=4507
Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
---
 include/sysemu/os-posix.h |  1 +
 include/sysemu/os-win32.h |  5 +++++
 os-posix.c                | 22 ++++++++++++++++++++++
 softmmu/vl.c              |  2 ++
 4 files changed, 30 insertions(+)

diff --git a/include/sysemu/os-posix.h b/include/sysemu/os-posix.h
index 1030d39904..edc415aff5 100644
--- a/include/sysemu/os-posix.h
+++ b/include/sysemu/os-posix.h
@@ -48,6 +48,7 @@ void os_setup_early_signal_handling(void);
 void os_set_proc_name(const char *s);
 void os_setup_signal_handling(void);
 void os_daemonize(void);
+void os_setup_limits(void);
 void os_setup_post(void);
 int os_mlock(void);
 
diff --git a/include/sysemu/os-win32.h b/include/sysemu/os-win32.h
index 91aa0d7ec0..f6e23fe01e 100644
--- a/include/sysemu/os-win32.h
+++ b/include/sysemu/os-win32.h
@@ -129,6 +129,11 @@ static inline int os_mlock(void)
     return -ENOSYS;
 }
 
+void os_setup_limits(void)
+{
+    return;
+}
+
 #define fsync _commit
 
 #if !defined(lseek)
diff --git a/os-posix.c b/os-posix.c
index cfcb96533c..0cc1d991b1 100644
--- a/os-posix.c
+++ b/os-posix.c
@@ -24,6 +24,7 @@
  */
 
 #include "qemu/osdep.h"
+#include <sys/resource.h>
 #include <sys/wait.h>
 #include <pwd.h>
 #include <grp.h>
@@ -286,6 +287,27 @@ void os_daemonize(void)
     }
 }
 
+void os_setup_limits(void)
+{
+    struct rlimit nofile;
+
+    if (getrlimit(RLIMIT_NOFILE, &nofile) < 0) {
+        warn_report("unable to query NOFILE limit: %s", strerror(errno));
+        return;
+    }
+
+    if (nofile.rlim_cur == nofile.rlim_max) {
+        return;
+    }
+
+    nofile.rlim_cur = nofile.rlim_max;
+
+    if (setrlimit(RLIMIT_NOFILE, &nofile) < 0) {
+        warn_report("unable to set NOFILE limit: %s", strerror(errno));
+        return;
+    }
+}
+
 void os_setup_post(void)
 {
     int fd = 0;
diff --git a/softmmu/vl.c b/softmmu/vl.c
index c9e9ede237..ba6ad8a8df 100644
--- a/softmmu/vl.c
+++ b/softmmu/vl.c
@@ -2713,6 +2713,8 @@ void qemu_init(int argc, char **argv)
     error_init(argv[0]);
     qemu_init_exec_dir(argv[0]);
 
+    os_setup_limits();
+
     qemu_init_arch_modules();
 
     qemu_init_subsystems();
