+#include <sys/ipc.h>
+#include <sys/sem.h>
+#include <sys/shm.h>
+
+/* our shared key */
+#define KEY_ID ((long)0x414e4547) /* "GENA" */
+
+// Semaphore operation structures
+static struct shbuf_ds {
+ int size; // size of data written
+ int head; // start of message list
+ int tail; // end of message list
+ char data[1]; // data/messages
+} *shbuf = NULL; // shared memory pointer
+
+static struct sembuf SMwup[1] = { {1, -1, IPC_NOWAIT} }; // set SMwup
+static struct sembuf SMwdn[3] = { {0, 0}, {1, 0}, {1, +1} }; // set SMwdn
+
+static int shmid = -1; // ipc shared memory id
+static int s_semid = -1; // ipc semaphore id
+static int shm_size = ((CONFIG_FEATURE_IPC_SYSLOG_BUFFER_SIZE)*1024); // default shm size
+
+static void ipcsyslog_cleanup(void)
+{
+ puts("Exiting syslogd!");
+ if (shmid != -1) {
+ shmdt(shbuf);
+ }
+
+ if (shmid != -1) {
+ shmctl(shmid, IPC_RMID, NULL);
+ }
+ if (s_semid != -1) {
+ semctl(s_semid, 0, IPC_RMID, 0);
+ }
+}
+
+static void ipcsyslog_init(void)
+{
+ if (shbuf == NULL) {
+ shmid = shmget(KEY_ID, shm_size, IPC_CREAT | 1023);
+ if (shmid == -1) {
+ bb_perror_msg_and_die("shmget");
+ }
+
+ shbuf = shmat(shmid, NULL, 0);
+ if (!shbuf) {
+ bb_perror_msg_and_die("shmat");
+ }
+
+ shbuf->size = shm_size - sizeof(*shbuf);
+ shbuf->head = shbuf->tail = 0;
+
+ // we'll trust the OS to set initial semval to 0 (let's hope)
+ s_semid = semget(KEY_ID, 2, IPC_CREAT | IPC_EXCL | 1023);
+ if (s_semid == -1) {
+ if (errno == EEXIST) {
+ s_semid = semget(KEY_ID, 2, 0);
+ if (s_semid == -1) {
+ bb_perror_msg_and_die("semget");
+ }
+ } else {
+ bb_perror_msg_and_die("semget");
+ }
+ }
+ } else {
+ printf("Buffer already allocated just grab the semaphore?");
+ }
+}
+
+/* write message to buffer */
+static void circ_message(const char *msg)
+{
+ int l = strlen(msg) + 1; /* count the whole message w/ '\0' included */
+ const char * const fail_msg = "Can't find the terminator token%s?\n";
+
+ if (semop(s_semid, SMwdn, 3) == -1) {
+ bb_perror_msg_and_die("SMwdn");
+ }
+
+ /*
+ * Circular Buffer Algorithm:
+ * --------------------------
+ *
+ * Start-off w/ empty buffer of specific size SHM_SIZ
+ * Start filling it up w/ messages. I use '\0' as separator to break up messages.
+ * This is also very handy since we can do printf on message.
+ *
+ * Once the buffer is full we need to get rid of the first message in buffer and
+ * insert the new message. (Note: if the message being added is >1 message then
+ * we will need to "remove" >1 old message from the buffer). The way this is done
+ * is the following:
+ * When we reach the end of the buffer we set a mark and start from the beginning.
+ * Now what about the beginning and end of the buffer? Well we have the "head"
+ * index/pointer which is the starting point for the messages and we have "tail"
+ * index/pointer which is the ending point for the messages. When we "display" the
+ * messages we start from the beginning and continue until we reach "tail". If we
+ * reach end of buffer, then we just start from the beginning (offset 0). "head" and
+ * "tail" are actually offsets from the beginning of the buffer.
+ *
+ * Note: This algorithm uses Linux IPC mechanism w/ shared memory and semaphores to provide
+ * a threadsafe way of handling shared memory operations.
+ */
+ if ((shbuf->tail + l) < shbuf->size) {
+ /* before we append the message we need to check the HEAD so that we won't
+ overwrite any of the message that we still need and adjust HEAD to point
+ to the next message! */
+ if (shbuf->tail < shbuf->head) {
+ if ((shbuf->tail + l) >= shbuf->head) {
+ /* we need to move the HEAD to point to the next message
+ * Theoretically we have enough room to add the whole message to the
+ * buffer, because of the first outer IF statement, so we don't have
+ * to worry about overflows here!
+ */
+ /* we need to know how many bytes we are overwriting to make enough room */
+ int k = shbuf->tail + l - shbuf->head;
+ char *c =
+ memchr(shbuf->data + shbuf->head + k, '\0',
+ shbuf->size - (shbuf->head + k));
+ if (c != NULL) { /* do a sanity check just in case! */
+ /* we need to convert pointer to offset + skip the '\0'
+ since we need to point to the beginning of the next message */
+ shbuf->head = c - shbuf->data + 1;
+ /* Note: HEAD is only used to "retrieve" messages, it's not used
+ when writing messages into our buffer */
+ } else { /* show an error message to know we messed up? */
+ printf(fail_msg,"");
+ shbuf->head = 0;
+ }
+ }
+ }
+
+ /* in other cases no overflows have been done yet, so we don't care! */
+ /* we should be ok to append the message now */
+ strncpy(shbuf->data + shbuf->tail, msg, l); /* append our message */
+ shbuf->tail += l; /* count full message w/ '\0' terminating char */
+ } else {
+ /* we need to break up the message and "circle" it around */
+ char *c;
+ int k = shbuf->tail + l - shbuf->size; /* count # of bytes we don't fit */
+
+ /* We need to move HEAD! This is always the case since we are going
+ * to "circle" the message. */
+ c = memchr(shbuf->data + k, '\0', shbuf->size - k);
+
+ if (c != NULL) { /* if we don't have '\0'??? weird!!! */
+ /* move head pointer */
+ shbuf->head = c - shbuf->data + 1;
+
+ /* now write the first part of the message */
+ strncpy(shbuf->data + shbuf->tail, msg, l - k - 1);
+
+ /* ALWAYS terminate end of buffer w/ '\0' */
+ shbuf->data[shbuf->size - 1] = '\0';
+
+ /* now write out the rest of the string to the beginning of the buffer */
+ strcpy(shbuf->data, &msg[l - k - 1]);
+
+ /* we need to place the TAIL at the end of the message */
+ shbuf->tail = k + 1;
+ } else {
+ printf(fail_msg, " from the beginning");
+ shbuf->head = shbuf->tail = 0; /* reset buffer, since it's probably corrupted */
+ }
+
+ }
+ if (semop(s_semid, SMwup, 1) == -1) {
+ bb_perror_msg_and_die("SMwup");
+ }
+
+}
+#else
+void ipcsyslog_cleanup(void);
+void ipcsyslog_init(void);
+void circ_message(const char *msg);
+#endif /* CONFIG_FEATURE_IPC_SYSLOG */
+