dmesg: fix kmsg read if read returns EPIPE

The /dev/kmsg can return EPIPE if current record has beed modified
while reading.

For init_kmsg, it cause switch to DMESG_METHOD_SYSLOG
(which is not expected) and later it can truncate output.

Signed-off-by: Milan Broz <mbroz@redhat.com>

diff --git a/sys-utils/dmesg.c b/sys-utils/dmesg.c
index e92904f64033d2c72390e156451edb34952ce34a..0ee03eebaef4b8a8e732e354e298e7de6525598b 100644 (file)
--- a/sys-utils/dmesg.c
+++ b/sys-utils/dmesg.c
@@ -851,6 +851,19 @@ static void print_buffer(struct dmesg_control *ctl,
                print_record(ctl, &rec);
 }
 
+static ssize_t read_kmsg_one(struct dmesg_control *ctl)
+{
+       ssize_t size;
+
+       /* kmsg returns EPIPE if record was modified while reading */
+       do {
+               size = read(ctl->kmsg, ctl->kmsg_buf,
+                           sizeof(ctl->kmsg_buf) - 1);
+       } while (size < 0 && errno == EPIPE);
+
+       return size;
+}
+
 static int init_kmsg(struct dmesg_control *ctl)
 {
        int mode = O_RDONLY;
@@ -877,8 +890,7 @@ static int init_kmsg(struct dmesg_control *ctl)
         * Let's try to read the first record. The record is later processed in
         * read_kmsg().
         */
-       ctl->kmsg_first_read = read(ctl->kmsg, ctl->kmsg_buf,
-                                 sizeof(ctl->kmsg_buf) - 1);
+       ctl->kmsg_first_read = read_kmsg_one(ctl);
        if (ctl->kmsg_first_read < 0) {
                close(ctl->kmsg);
                ctl->kmsg = -1;
@@ -996,7 +1008,7 @@ static int read_kmsg(struct dmesg_control *ctl)
                                      ctl->kmsg_buf, (size_t) sz) == 0)
                        print_record(ctl, &rec);
 
-               sz = read(ctl->kmsg, ctl->kmsg_buf, sizeof(ctl->kmsg_buf) - 1);
+               sz = read_kmsg_one(ctl);
        }
 
        return 0;