syslogd,logread: get rid of head pointer, fix logread bug in the process
authorDenis Vlasenko <vda.linux@googlemail.com>
Sun, 12 Aug 2007 21:33:06 +0000 (21:33 -0000)
committerDenis Vlasenko <vda.linux@googlemail.com>
Sun, 12 Aug 2007 21:33:06 +0000 (21:33 -0000)
function                                             old     new   delta
logread_main                                         450     462     +12
syslogd_main                                        1246    1252      +6
shbuf                                                  -       4      +4
buf                                                   34      30      -4
packed_usage                                       22729   22724      -5
log_locally                                          957     767    -190
------------------------------------------------------------------------------
(add/remove: 1/0 grow/shrink: 2/3 up/down: 22/-199)          Total: -177 bytes
   text    data     bss     dec     hex filename
 773886    1116   11316  786318   bff8e busybox_old
 773714    1116   11316  786146   bfee2 busybox_unstripped

include/usage.h
sysklogd/logread.c
sysklogd/syslogd.c

index 9c14f4508600713f4b95625bba7fadf5fe73e956..3f2916006f53186a38dcf03a4b6dc850b30d7282 100644 (file)
@@ -3327,17 +3327,17 @@ USE_FEATURE_RUN_PARTS_FANCY("\n -l      Prints names of all matching files even when
        "Note that this version of syslogd ignores /etc/syslog.conf." \
        "\n\nOptions:" \
        "\n     -n              Run as foreground process" \
-       "\n     -O FILE         Use an alternate log file (default=/var/log/messages)" \
-       "\n     -l n            Sets the local log level of messages to n" \
-       "\n     -S              Make logging output smaller" \
+       "\n     -O FILE         Log to given file (default=/var/log/messages)" \
+       "\n     -l n            Set local log level" \
+       "\n     -S              Smaller logging output" \
        USE_FEATURE_ROTATE_LOGFILE( \
        "\n     -s SIZE         Max size (KB) before rotate (default=200KB, 0=off)" \
        "\n     -b NUM          Number of rotated logs to keep (default=1, max=99, 0=purge)") \
        USE_FEATURE_REMOTE_LOG( \
        "\n     -R HOST[:PORT]  Log to IP or hostname on PORT (default PORT=514/UDP)" \
-       "\n     -L              Log locally and via network logging (default is network only)") \
+       "\n     -L              Log locally and via network (default is network only if -R)") \
        USE_FEATURE_IPC_SYSLOG( \
-       "\n     -C[size(KiB)]   Log to a shared mem buffer (read the buffer using logread)")
+       "\n     -C[size(KiB)]   Log to shared mem buffer (read it using logread)")
        /* NB: -Csize shouldn't have space (because size is optional) */
 /*     "\n     -m MIN          Minutes between MARK lines (default=20, 0=off)" */
 #define syslogd_example_usage \
index ac354b5c3d5775d95b33779b86c88de85b11c5d5..597e285a52c132e3528eea43bfbb0de9865f32db 100644 (file)
 enum { KEY_ID = 0x414e4547 }; /* "GENA" */
 
 static struct shbuf_ds {
-       int32_t size;           // size of data written
-       int32_t head;           // start of message list
+       int32_t size;           // size of data - 1
        int32_t tail;           // end of message list
-       char data[1];           // data/messages
-} *buf;                         // shared memory pointer
+       char data[1];           // messages
+} *shbuf;
 
 // Semaphore operation structures
 static struct sembuf SMrup[1] = {{0, -1, IPC_NOWAIT | SEM_UNDO}}; // set SMrup
@@ -34,7 +33,7 @@ static void error_exit(const char *str) ATTRIBUTE_NORETURN;
 static void error_exit(const char *str)
 {
        //release all acquired resources
-       shmdt(buf);
+       shmdt(shbuf);
        bb_perror_msg_and_die(str);
 }
 
@@ -50,7 +49,7 @@ static void sem_up(int semid)
 static void interrupted(int sig ATTRIBUTE_UNUSED)
 {
        signal(SIGINT, SIG_IGN);
-       shmdt(buf);
+       shmdt(shbuf);
        exit(0);
 }
 
@@ -66,79 +65,105 @@ int logread_main(int argc, char **argv)
        if (log_shmid == -1)
                bb_perror_msg_and_die("can't find syslogd buffer");
 
-       // Attach shared memory to our char*
-       buf = shmat(log_shmid, NULL, SHM_RDONLY);
-       if (buf == NULL)
+       /* Attach shared memory to our char* */
+       shbuf = shmat(log_shmid, NULL, SHM_RDONLY);
+       if (shbuf == NULL)
                bb_perror_msg_and_die("can't access syslogd buffer");
 
        log_semid = semget(KEY_ID, 0, 0);
        if (log_semid == -1)
                error_exit("can't get access to semaphores for syslogd buffer");
 
-       // attempt to redefine ^C signal
        signal(SIGINT, interrupted);
 
-       // Suppose atomic memory move
-       cur = follow ? buf->tail : buf->head;
+       /* Suppose atomic memory read */
+       /* Max possible value for tail is shbuf->size - 1 */
+       cur = shbuf->tail;
 
+       /* Loop for logread -f, one pass if there was no -f */
        do {
+               unsigned shbuf_size;
+               unsigned shbuf_tail;
+               const char *shbuf_data;
 #if ENABLE_FEATURE_LOGREAD_REDUCED_LOCKING
-               char *buf_data;
-               int log_len, j;
+               int i;
+               int len_first_part;
+               int len_total = len_total; /* for gcc */
+               char *copy = copy; /* for gcc */
 #endif
                if (semop(log_semid, SMrdn, 2) == -1)
                        error_exit("semop[SMrdn]");
 
-               if (DEBUG)
-                       printf("head:%i cur:%d tail:%i size:%i\n",
-                                       buf->head, cur, buf->tail, buf->size);
+               /* Copy the info, helps gcc to realize that it doesn't change */
+               shbuf_size = shbuf->size;
+               shbuf_tail = shbuf->tail;
+               shbuf_data = shbuf->data; /* pointer! */
 
-               if (buf->head == buf->tail || cur == buf->tail) {
-                       if (follow) {
+               if (DEBUG)
+                       printf("cur:%d tail:%i size:%i\n",
+                                       cur, shbuf_tail, shbuf_size);
+
+               if (!follow) {
+                       /* advance to oldest complete message */
+                       /* find NUL */
+                       cur += strlen(shbuf_data + cur);
+                       if (cur >= shbuf_size) { /* last byte in buffer? */
+                               cur = strnlen(shbuf_data, shbuf_tail);
+                               if (cur == shbuf_tail)
+                                       goto unlock; /* no complete messages */
+                       }
+                       /* advance to first byte of the message */
+                       cur++;
+                       if (cur >= shbuf_size) /* last byte in buffer? */
+                               cur = 0;
+               } else { /* logread -f */
+                       if (cur == shbuf_tail) {
                                sem_up(log_semid);
                                fflush(stdout);
                                sleep(1); /* TODO: replace me with a sleep_on */
                                continue;
                        }
-                       puts("<empty syslog>");
                }
 
-               // Read Memory
+               /* Read from cur to tail */
 #if ENABLE_FEATURE_LOGREAD_REDUCED_LOCKING
-               log_len = buf->tail - cur;
-               if (log_len < 0)
-                       log_len += buf->size;
-               buf_data = xmalloc(log_len);
-
-               if (buf->tail >= cur)
-                       j = log_len;
-               else
-                       j = buf->size - cur;
-               memcpy(buf_data, buf->data + cur, j);
-
-               if (buf->tail < cur)
-                       memcpy(buf_data + buf->size - cur, buf->data, buf->tail);
-               cur = buf->tail;
+               len_first_part = len_total = shbuf_tail - cur;
+               if (len_total < 0) {
+                       /* message wraps: */
+                       /* [SECOND PART.........FIRST PART] */
+                       /*  ^data      ^tail    ^cur      ^size */
+                       len_total += shbuf_size;
+               }
+               copy = xmalloc(len_total + 1);
+               if (len_first_part < 0) {
+                       /* message wraps (see above) */
+                       len_first_part = shbuf_size - cur;
+                       memcpy(copy + len_first_part, shbuf_data, shbuf_tail);
+               }
+               memcpy(copy, shbuf_data + cur, len_first_part);
+               copy[len_total] = '\0';
+               cur = shbuf_tail;
 #else
-               while (cur != buf->tail) {
-                       fputs(buf->data + cur, stdout);
-                       cur += strlen(buf->data + cur) + 1;
-                       if (cur >= buf->size)
+               while (cur != shbuf_tail) {
+                       fputs(shbuf_data + cur, stdout);
+                       cur += strlen(shbuf_data + cur) + 1;
+                       if (cur >= shbuf_size)
                                cur = 0;
                }
 #endif
-               // release the lock on the log chain
+ unlock:
+               /* release the lock on the log chain */
                sem_up(log_semid);
 
 #if ENABLE_FEATURE_LOGREAD_REDUCED_LOCKING
-               for (j = 0; j < log_len; j += strlen(buf_data+j) + 1) {
-                       fputs(buf_data + j, stdout);
+               for (i = 0; i < len_total; i += strlen(copy + i) + 1) {
+                       fputs(copy + i, stdout);
                }
-               free(buf_data);
+               free(copy);
 #endif
        } while (follow);
 
-       shmdt(buf);
+       shmdt(shbuf);
 
        fflush_stdout_and_exit(EXIT_SUCCESS);
 }
index 0ed16bc9eb6178e2b008555e0d3743f9658a38f5..6ecbd16f018c17498fbda581f365da5ae2d4de2f 100644 (file)
@@ -46,8 +46,7 @@ enum { MAX_READ = 256 };
 
 /* Semaphore operation structures */
 struct shbuf_ds {
-       int32_t size;   /* size of data written */
-       int32_t head;   /* start of message list */
+       int32_t size;   /* size of data - 1 */
        int32_t tail;   /* end of message list */
        char data[1];   /* data/messages */
 };
@@ -212,8 +211,9 @@ static void ipcsyslog_init(void)
                bb_perror_msg_and_die("shmat");
        }
 
-       G.shbuf->size = G.shm_size - offsetof(struct shbuf_ds, data);
-       G.shbuf->head = G.shbuf->tail = 0;
+       memset(G.shbuf, 0, G.shm_size);
+       G.shbuf->size = G.shm_size - offsetof(struct shbuf_ds, data) - 1;
+       /*G.shbuf->tail = 0;*/
 
        // we'll trust the OS to set initial semval to 0 (let's hope)
        G.s_semid = semget(KEY_ID, 2, IPC_CREAT | IPC_EXCL | 1023);
@@ -231,7 +231,6 @@ static void ipcsyslog_init(void)
 static void log_to_shmem(const char *msg, int len)
 {
        int old_tail, new_tail;
-       char *c;
 
        if (semop(G.s_semid, G.SMwdn, 3) == -1) {
                bb_perror_msg_and_die("SMwdn");
@@ -240,49 +239,20 @@ static void log_to_shmem(const char *msg, int len)
        /* Circular Buffer Algorithm:
         * --------------------------
         * tail == position where to store next syslog message.
-        * head == position of next message to retrieve ("print").
-        * if head == tail, there is no "unprinted" messages left.
-        * head is typically advanced by separate "reader" program,
-        * but if there isn't one, we have to do it ourself.
-        * messages are NUL-separated.
+        * tail's max value is (shbuf->size - 1)
+        * Last byte of buffer is never used and remains NUL.
         */
        len++; /* length with NUL included */
  again:
        old_tail = G.shbuf->tail;
        new_tail = old_tail + len;
        if (new_tail < G.shbuf->size) {
-               /* No need to move head if shbuf->head <= old_tail,
-                * else... */
-               if (old_tail < G.shbuf->head && G.shbuf->head <= new_tail) {
-                       /* ...need to move head forward */
-                       c = memchr(G.shbuf->data + new_tail, '\0',
-                                          G.shbuf->size - new_tail);
-                       if (!c) /* no NUL ahead of us, wrap around */
-                               c = memchr(G.shbuf->data, '\0', old_tail);
-                       if (!c) { /* still nothing? point to this msg... */
-                               G.shbuf->head = old_tail;
-                       } else {
-                               /* convert pointer to offset + skip NUL */
-                               G.shbuf->head = c - G.shbuf->data + 1;
-                       }
-               }
                /* store message, set new tail */
                memcpy(G.shbuf->data + old_tail, msg, len);
                G.shbuf->tail = new_tail;
        } else {
-               /* we need to break up the message and wrap it around */
                /* k == available buffer space ahead of old tail */
-               int k = G.shbuf->size - old_tail - 1;
-               if (G.shbuf->head > old_tail) {
-                       /* we are going to overwrite head, need to
-                        * move it out of the way */
-                       c = memchr(G.shbuf->data, '\0', old_tail);
-                       if (!c) { /* nothing? point to this msg... */
-                               G.shbuf->head = old_tail;
-                       } else { /* convert pointer to offset + skip NUL */
-                               G.shbuf->head = c - G.shbuf->data + 1;
-                       }
-               }
+               int k = G.shbuf->size - old_tail;
                /* copy what fits to the end of buffer, and repeat */
                memcpy(G.shbuf->data + old_tail, msg, k);
                msg += k;
@@ -294,7 +264,7 @@ static void log_to_shmem(const char *msg, int len)
                bb_perror_msg_and_die("SMwup");
        }
        if (DEBUG)
-               printf("head:%d tail:%d\n", G.shbuf->head, G.shbuf->tail);
+               printf("tail:%d\n", G.shbuf->tail);
 }
 #else
 void ipcsyslog_cleanup(void);
@@ -339,11 +309,10 @@ static void log_locally(char *msg)
                }
 #if ENABLE_FEATURE_ROTATE_LOGFILE
                {
-               struct stat statf;
-
-               G.isRegular = (fstat(G.logFD, &statf) == 0 && (statf.st_mode & S_IFREG));
-               /* bug (mostly harmless): can wrap around if file > 4gb */
-               G.curFileSize = statf.st_size;
+                       struct stat statf;
+                       G.isRegular = (fstat(G.logFD, &statf) == 0 && S_ISREG(statf.st_mode));
+                       /* bug (mostly harmless): can wrap around if file > 4gb */
+                       G.curFileSize = statf.st_size;
                }
 #endif
        }