logread: implement dumpfollow mode of operation

This is basically a combination of the default (dump mode) and -f
(follow mode). Specifying -F makes logread first dump the log buffer and
then immediately start following it.

function                                             old     new   delta
packed_usage                                       30412   30443     +31
logread_main                                         491     497      +6

Signed-off-by: Phil Sutter <phil.sutter@viprinet.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

diff --git a/sysklogd/logread.c b/sysklogd/logread.c
index bea73d9323955992e45ad62ca921b0fe46b692e6..da4a4d4dfc481b8798d06539b79e533605ac55bf 100644 (file)
--- a/sysklogd/logread.c
+++ b/sysklogd/logread.c
@@ -10,10 +10,11 @@
  */
 
 //usage:#define logread_trivial_usage
-//usage:       "[-f]"
+//usage:       "[-fF]"
 //usage:#define logread_full_usage "\n\n"
 //usage:       "Show messages in syslogd's circular buffer\n"
 //usage:     "\n       -f      Output data as log grows"
+//usage:     "\n       -F      Same as -f, but dump buffer first"
 
 #include "libbb.h"
 #include <sys/ipc.h>
@@ -83,7 +84,7 @@ int logread_main(int argc UNUSED_PARAM, char **argv)
        unsigned cur;
        int log_semid; /* ipc semaphore id */
        int log_shmid; /* ipc shared memory id */
-       smallint follow = getopt32(argv, "f");
+       int follow = getopt32(argv, "fF");
 
        INIT_G();
 
@@ -106,7 +107,7 @@ int logread_main(int argc UNUSED_PARAM, char **argv)
        /* Max possible value for tail is shbuf->size - 1 */
        cur = shbuf->tail;
 
-       /* Loop for logread -f, one pass if there was no -f */
+       /* Loop for -f or -F, one pass otherwise */
        do {
                unsigned shbuf_size;
                unsigned shbuf_tail;
@@ -129,7 +130,12 @@ int logread_main(int argc UNUSED_PARAM, char **argv)
                        printf("cur:%u tail:%u size:%u\n",
                                        cur, shbuf_tail, shbuf_size);
 
-               if (!follow) {
+               if (!(follow & 1)) { /* not -f */
+                       /* if -F, "convert" it to -f, so that we dont
+                        * dump the entire buffer on each iteration
+                        */
+                       follow >>= 1;
+
                        /* advance to oldest complete message */
                        /* find NUL */
                        cur += strlen(shbuf_data + cur);
@@ -142,7 +148,7 @@ int logread_main(int argc UNUSED_PARAM, char **argv)
                        cur++;
                        if (cur >= shbuf_size) /* last byte in buffer? */
                                cur = 0;
-               } else { /* logread -f */
+               } else { /* -f */
                        if (cur == shbuf_tail) {
                                sem_up(log_semid);
                                fflush_all();