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log: setlogmask(0) can actually result in a system call, don't use it

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Before commit 32d07f5e59 ("passt, pasta: Completely avoid dynamic
memory allocation"), we didn't store the current log mask in a
variable, and we fetched it using setlogmask(0) wherever needed.

But after that commit, we can use our log_mask copy instead. And we
should: with recent glibc versions, setlogmask(0) actually results in
a system call, which causes a substantial overhead with high transfer
rates: we use setlogmask(0) even to decide we don't want to print
debug messages.

Now that we rely on log_mask in early stages, before setlogmask() is
called, we need to initialise that variable to the special LOG_EMERG
mask value right away: define LOG_EARLY to make this clearer, and,
while at it, group conditions in vlogmsg() into something more terse.

Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
This commit is contained in:
Stefano Brivio 2024-02-02 00:22:16 +01:00
parent 78901eeae3
commit 7ee4e17267
2 changed files with 12 additions and 13 deletions

7
passt.c
View file

@ -251,9 +251,6 @@ int main(int argc, char **argv)
__openlog(log_name, 0, LOG_DAEMON);
/* Meaning we don't know yet: log everything. LOG_EMERG is unused */
__setlogmask(LOG_MASK(LOG_EMERG));
c.epollfd = epoll_create1(EPOLL_CLOEXEC);
if (c.epollfd == -1) {
perror("epoll_create1");
@ -322,8 +319,8 @@ int main(int argc, char **argv)
if (isolate_prefork(&c))
die("Failed to sandbox process, exiting");
/* Once the log mask is not LOG_EMERG, we will no longer
* log to stderr if there was a log file specified.
/* Once the log mask is not LOG_EARLY, we will no longer log to stderr
* if there was a log file specified.
*/
if (c.debug)
__setlogmask(LOG_UPTO(LOG_DEBUG));