From: Yu Watanabe <watanabe.yu+github@gmail.com>
Date: Mon, 14 Apr 2025 19:34:40 +0000 (+0900)
Subject: journal/kmsg: drop support old kernels (<3.5) without reading /dev/kmsg support
X-Git-Tag: v258-rc1~816^2~3
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=da741d9fd9fe5897209b9f569a42acd00865ed68;p=thirdparty%2Fsystemd.git

journal/kmsg: drop support old kernels (<3.5) without reading /dev/kmsg support

/dev/kmsg is readable since kernel v3.5:
https://github.com/torvalds/linux/commit/e11fea92e13fb91c50bacca799a6131c81929986

Now our baseline on the kernel is v5.4. Let's assume /dev/kmsg is always
readable.
---

diff --git a/src/journal/journald-kmsg.c b/src/journal/journald-kmsg.c
index 86115ad70da..2f41c549255 100644
--- a/src/journal/journald-kmsg.c
+++ b/src/journal/journald-kmsg.c
@@ -325,14 +325,6 @@ static int server_read_dev_kmsg(Server *s) {
         if (l == 0)
                 return 0;
         if (l < 0) {
-                /* Old kernels which don't allow reading from /dev/kmsg return EINVAL when we try. So handle
-                 * this cleanly, but don't try to ever read from it again. */
-                if (errno == EINVAL) {
-                        s->dev_kmsg_event_source = sd_event_source_unref(s->dev_kmsg_event_source);
-                        s->dev_kmsg_readable = false;
-                        return 0;
-                }
-
                 if (ERRNO_IS_TRANSIENT(errno) || errno == EPIPE)
                         return 0;
 
@@ -403,11 +395,6 @@ int server_open_dev_kmsg(Server *s) {
                 return 0;
 
         r = sd_event_add_io(s->event, &s->dev_kmsg_event_source, s->dev_kmsg_fd, EPOLLIN, dispatch_dev_kmsg, s);
-        if (r == -EPERM) { /* This will fail with EPERM on older kernels where /dev/kmsg is not readable. */
-                log_debug_errno(r, "Not reading from /dev/kmsg since that's not supported, apparently.");
-                r = 0;
-                goto finish;
-        }
         if (r < 0) {
                 log_error_errno(r, "Failed to add /dev/kmsg fd to event loop: %m");
                 goto finish;