158 lines
3.7 KiB
Diff
158 lines
3.7 KiB
Diff
From 453a7611b625fc6f306a47ccc61bf3b83d75e522 Mon Sep 17 00:00:00 2001
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From: "Richard W.M. Jones" <rjones@redhat.com>
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Date: Thu, 5 Aug 2021 10:13:53 +0100
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Subject: [PATCH] server: Make debug messages atomic
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Previously we used flockfile around the separate fprintf statements
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used to emit debug messages. However this does not make debug
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messages atomic (only atomic with respect to other nbdkit threads).
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It's easy to see this in strace:
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1915655 write(2, "nbdkit: ", 8) = 8
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1915655 write(2, "debug: ", 7) = 7
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1915655 write(2, "nbdkit 1.27.3 (nbdkit-1.27.3-1.f"..., 36) = 36
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1915655 write(2, "\n", 1) = 1
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We require open_memstream already, so use this to print messages to a
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string buffer which we can emit in a single write.
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This fixes various tests which grep the log file looking for sentinel
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messages. In particular a recent Fedora build failure in
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test-nbdkit-backend-debug.sh was caused by this, but there are other
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tests that fail occasionally for the same reason.
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This change also tries harder to set errno correctly before expanding
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the format string (for debug messages that contain %m).
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Note that libnbd already emits atomic messages.
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(cherry picked from commit 30eef3bf2d93b12072f91f95987bae33f9e3fe1a)
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---
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server/debug.c | 72 ++++++++++++++++++++++++++++++++------------------
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1 file changed, 46 insertions(+), 26 deletions(-)
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diff --git a/server/debug.c b/server/debug.c
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index eede5e16..07710581 100644
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--- a/server/debug.c
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+++ b/server/debug.c
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@@ -40,23 +40,22 @@
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#include "internal.h"
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-/* Called with flockfile (stderr) taken. */
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static void
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-prologue (void)
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+prologue (FILE *fp)
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{
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const char *name = threadlocal_get_name ();
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size_t instance_num = threadlocal_get_instance_num ();
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- fprintf (stderr, "%s: ", program_name);
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+ fprintf (fp, "%s: ", program_name);
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if (name) {
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- fprintf (stderr, "%s", name);
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+ fprintf (fp, "%s", name);
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if (instance_num > 0)
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- fprintf (stderr, "[%zu]", instance_num);
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- fprintf (stderr, ": ");
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+ fprintf (fp, "[%zu]", instance_num);
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+ fprintf (fp, ": ");
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}
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- fprintf (stderr, "debug: ");
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+ fprintf (fp, "debug: ");
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}
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/* Note: preserves the previous value of errno. */
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@@ -64,20 +63,30 @@ NBDKIT_DLL_PUBLIC void
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nbdkit_vdebug (const char *fs, va_list args)
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{
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int err = errno;
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+ CLEANUP_FREE char *str = NULL;
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+ size_t len = 0;
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+ FILE *fp;
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if (!verbose)
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return;
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-#ifdef HAVE_FLOCKFILE
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- flockfile (stderr);
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-#endif
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- prologue ();
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- vfprintf (stderr, fs, args);
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+ fp = open_memstream (&str, &len);
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+ if (fp == NULL) {
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+ /* Try to emit what we can. */
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+ errno = err;
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+ vfprintf (stderr, fs, args);
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+ return;
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+ }
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- fprintf (stderr, "\n");
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-#ifdef HAVE_FUNLOCKFILE
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- funlockfile (stderr);
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-#endif
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+ prologue (fp);
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+
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+ errno = err;
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+ vfprintf (fp, fs, args);
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+
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+ fprintf (fp, "\n");
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+ fclose (fp);
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+
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+ fputs (str, stderr);
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errno = err;
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}
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@@ -86,25 +95,36 @@ nbdkit_vdebug (const char *fs, va_list args)
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NBDKIT_DLL_PUBLIC void
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nbdkit_debug (const char *fs, ...)
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{
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+ int err = errno;
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va_list args;
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- int err = errno;
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+ CLEANUP_FREE char *str = NULL;
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+ size_t len = 0;
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+ FILE *fp;
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if (!verbose)
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return;
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-#ifdef HAVE_FLOCKFILE
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- flockfile (stderr);
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-#endif
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- prologue ();
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+ fp = open_memstream (&str, &len);
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+ if (fp == NULL) {
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+ /* Try to emit what we can. */
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+ va_start (args, fs);
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+ errno = err;
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+ vfprintf (stderr, fs, args);
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+ va_end (args);
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+ return;
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+ }
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+
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+ prologue (fp);
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va_start (args, fs);
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- vfprintf (stderr, fs, args);
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+ errno = err;
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+ vfprintf (fp, fs, args);
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va_end (args);
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- fprintf (stderr, "\n");
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-#ifdef HAVE_FUNLOCKFILE
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- funlockfile (stderr);
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-#endif
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+ fprintf (fp, "\n");
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+ fclose (fp);
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+
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+ fputs (str, stderr);
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errno = err;
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}
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--
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2.31.1
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