94 lines
2.8 KiB
Diff
94 lines
2.8 KiB
Diff
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From bfa6d4064cb74f429149d14ab4025b258fc95ec4 Mon Sep 17 00:00:00 2001
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From: "Richard W.M. Jones" <rjones@redhat.com>
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Date: Tue, 23 Jul 2024 15:28:06 +0100
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Subject: [PATCH] server: Take a thread-local copy of the last call to
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nbdkit_error
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nbdkit_error has traditionally been a "fancy wrapper around fprintf"
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(kind of, don't take that literally). It is encouraged that plugins
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and filters do something like:
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if (error) {
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nbdkit_error ("oops, a bad thing happened");
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return -1;
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}
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but we don't enforce this. Plugins might call nbdkit_error more than
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once or not at all.
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The point where we get to sending an error back over the wire to the
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NBD client is long after the plugin returned above, and after
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nbdkit_error was called.
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Therefore in order to send errors back to the NBD client, we must keep
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the last error message around.
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This change simply modifies nbdkit_error to make a best-effort attempt
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to save the last error message in thread-local storage.
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We also clear the last error when a new request starts, to ensure that
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we don't leak errors across different callbacks or connections.
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---
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server/log.c | 21 +++++++++++++++++++++
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server/protocol.c | 5 +++++
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2 files changed, 26 insertions(+)
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diff --git a/server/log.c b/server/log.c
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index 9c1f667a..acf14d57 100644
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--- a/server/log.c
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+++ b/server/log.c
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@@ -40,6 +40,25 @@
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#include "internal.h"
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+/* Copy the error message to threadlocal. This is sent to callers
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+ * which are using structured replies, but is for extra information
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+ * only so don't fail if we are unable to copy it.
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+ */
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+static void
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+copy_error_to_threadlocal (int orig_errno, const char *fs, va_list args)
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+{
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+ va_list args_copy;
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+ char *msg;
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+ int r;
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+
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+ va_copy (args_copy, args);
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+ errno = orig_errno; /* must restore in case fs contains %m */
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+ r = vasprintf (&msg, fs, args_copy);
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+ va_end (args_copy);
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+ if (r != -1 && msg)
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+ threadlocal_set_last_error (msg); /* ownership passed to threadlocal */
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+}
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+
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/* Call the right log_*_verror function depending on log_sink.
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* Note: preserves the previous value of errno.
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*/
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@@ -48,6 +67,8 @@ log_verror (const char *fs, va_list args)
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{
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int orig_errno = errno;
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+ copy_error_to_threadlocal (orig_errno, fs, args);
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+
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switch (log_to) {
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case LOG_TO_DEFAULT:
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if (forked_into_background)
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diff --git a/server/protocol.c b/server/protocol.c
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index 677da05c..d428bfc8 100644
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--- a/server/protocol.c
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+++ b/server/protocol.c
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@@ -239,6 +239,11 @@ handle_request (uint16_t cmd, uint16_t flags, uint64_t offset, uint32_t count,
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*/
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threadlocal_set_errno (0);
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+ /* Also clear the last error in this thread so we will only save
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+ * nbdkit_error() from this request.
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+ */
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+ threadlocal_clear_last_error ();
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+
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switch (cmd) {
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case NBD_CMD_READ:
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if (backend_pread (c, buf, count, offset, 0, &err) == -1)
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--
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2.43.0
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