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journalcl: simplify handling of stdout being a regular file and epoll()

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Let's not check the fd type beforehand, let's instead gracefully handle
if we get EPERM back from epoll_ctl() because the fd doesn't do epoll.
THis should be safer and more generic.

The epoll_ctl(2) man page clearly documents EPERM is being returned in
this case, hence it's safe to check for exactly that case.

Follow-up for: #28644
This commit is contained in:
Lennart Poettering
2023-08-10 14:47:12 +02:00
parent e5e900edcd
commit 9050632ec0
1 changed files with 9 additions and 10 deletions
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19
src/journal/journalctl.c
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@@ -2310,7 +2310,6 @@ static int on_signal(sd_event_source *s, const struct signalfd_siginfo *si, void
static int setup_event(Context *c, int fd, sd_event **ret) {
_cleanup_(sd_event_unrefp) sd_event *e = NULL;
struct stat st;
int r;
assert(arg_follow);
@@ -2329,15 +2328,15 @@ static int setup_event(Context *c, int fd, sd_event **ret) {
if (r < 0)
return log_error_errno(r, "Failed to add io event source for journal: %m");
if (fstat(STDOUT_FILENO, &st) < 0)
return log_error_errno(errno, "Failed to stat stdout: %m");
if (IN_SET(st.st_mode & S_IFMT, S_IFCHR, S_IFIFO, S_IFSOCK)) {
/* Also keeps an eye on STDOUT, and exits as soon as we see a POLLHUP on that, i.e. when it is closed. */
r = sd_event_add_io(e, NULL, STDOUT_FILENO, EPOLLHUP|EPOLLERR, NULL, INT_TO_PTR(-ECANCELED));
if (r < 0)
return log_error_errno(r, "Failed to add io event source for stdout: %m");
}
/* Also keeps an eye on STDOUT, and exits as soon as we see a POLLHUP on that, i.e. when it is closed. */
r = sd_event_add_io(e, NULL, STDOUT_FILENO, EPOLLHUP|EPOLLERR, NULL, INT_TO_PTR(-ECANCELED));
if (r == -EPERM)
/* Installing an epoll watch on a regular file doesn't work and fails with EPERM. Which is
* totally OK, handle it gracefully. epoll_ctl() documents EPERM as the error returned when
* the specified fd doesn't support epoll, hence it's safe to check for that. */
log_debug_errno(r, "Unable to install EPOLLHUP watch on stderr, not watching for hangups.");
else if (r < 0)
return log_error_errno(r, "Failed to add io event source for stdout: %m");
if (arg_lines != 0 || arg_since_set) {
r = sd_event_add_defer(e, NULL, on_first_event, c);