Implement file-backed ring buffer

[lttng-ust.git] / libringbuffer / ring_buffer_backend.c

diff --git a/libringbuffer/ring_buffer_backend.c b/libringbuffer/ring_buffer_backend.c
index ae8365227c3405fcb39aad8a32eba3e5d730be14..3a667adce53c8ccdda4f15b872c13d054907f7ed 100644 (file)
--- a/libringbuffer/ring_buffer_backend.c
+++ b/libringbuffer/ring_buffer_backend.c
@@ -29,6 +29,8 @@
 #include "smp.h"
 #include "shm.h"
 
+#define UINT_MAX_STR_LEN 11    /* includes \0 */
+
 /**
  * lib_ring_buffer_backend_allocate - allocate a channel buffer
  * @config: ring buffer instance configuration
@@ -115,7 +117,6 @@ int lib_ring_buffer_backend_allocate(const struct lttng_ust_lib_ring_buffer_conf
                        mmap_offset += subbuf_size;
                }
        }
-
        return 0;
 
 free_array:
@@ -199,6 +200,7 @@ void channel_backend_reset(struct channel_backend *chanb)
  * @subbuf_size: size of sub-buffers (> PAGE_SIZE, power of 2)
  * @num_subbuf: number of sub-buffers (power of 2)
  * @lttng_ust_shm_handle: shared memory handle
+ * @shm_path: shared memory files path
  *
  * Returns channel pointer if successful, %NULL otherwise.
  *
@@ -212,7 +214,8 @@ int channel_backend_init(struct channel_backend *chanb,
                         const char *name,
                         const struct lttng_ust_lib_ring_buffer_config *config,
                         size_t subbuf_size, size_t num_subbuf,
-                        struct lttng_ust_shm_handle *handle)
+                        struct lttng_ust_shm_handle *handle,
+                        const char *shm_path)
 {
        struct channel *chan = caa_container_of(chanb, struct channel, backend);
        unsigned int i;
@@ -234,6 +237,12 @@ int channel_backend_init(struct channel_backend *chanb,
                return -EINVAL;
        if (!num_subbuf || (num_subbuf & (num_subbuf - 1)))
                return -EINVAL;
+       /*
+        * Overwrite mode buffers require at least 2 subbuffers per
+        * buffer.
+        */
+       if (config->mode == RING_BUFFER_OVERWRITE && num_subbuf < 2)
+               return -EINVAL;
 
        ret = subbuffer_id_check_index(config, num_subbuf);
        if (ret)
@@ -279,8 +288,21 @@ int channel_backend_init(struct channel_backend *chanb,
                 */
                for_each_possible_cpu(i) {
                        struct shm_object *shmobj;
-
-                       shmobj = shm_object_table_append(handle->table, shmsize);
+                       char shm_buf_path[PATH_MAX];
+
+                       if (shm_path) {
+                               char cpu_nr[UINT_MAX_STR_LEN];  /* unsigned int max len */
+
+                               strncpy(shm_buf_path, shm_path, PATH_MAX);
+                               shm_buf_path[PATH_MAX - 1] = '\0';
+                               ret = snprintf(cpu_nr, UINT_MAX_STR_LEN, "%u", i);
+                               if (ret != 1)
+                                       goto end;
+                               strncat(shm_buf_path, cpu_nr,
+                                       PATH_MAX - strlen(shm_buf_path) - 1);
+                       }
+                       shmobj = shm_object_table_alloc(handle->table, shmsize,
+                                       SHM_OBJECT_SHM, shm_path ? shm_buf_path : NULL);
                        if (!shmobj)
                                goto end;
                        align_shm(shmobj, __alignof__(struct lttng_ust_lib_ring_buffer));
@@ -298,7 +320,8 @@ int channel_backend_init(struct channel_backend *chanb,
                struct shm_object *shmobj;
                struct lttng_ust_lib_ring_buffer *buf;
 
-               shmobj = shm_object_table_append(handle->table, shmsize);
+               shmobj = shm_object_table_alloc(handle->table, shmsize,
+                                       SHM_OBJECT_SHM, shm_path);
                if (!shmobj)
                        goto end;
                align_shm(shmobj, __alignof__(struct lttng_ust_lib_ring_buffer));
@@ -379,8 +402,9 @@ size_t lib_ring_buffer_read(struct lttng_ust_lib_ring_buffer_backend *bufb, size
  * @dest : destination address
  * @len : destination's length
  *
- * return string's length
+ * Return string's length, or -EINVAL on error.
  * Should be protected by get_subbuf/put_subbuf.
+ * Destination length should be at least 1 to hold '\0'.
  */
 int lib_ring_buffer_read_cstr(struct lttng_ust_lib_ring_buffer_backend *bufb, size_t offset,
                              void *dest, size_t len, struct lttng_ust_shm_handle *handle)
@@ -392,6 +416,8 @@ int lib_ring_buffer_read_cstr(struct lttng_ust_lib_ring_buffer_backend *bufb, si
        struct lttng_ust_lib_ring_buffer_backend_pages_shmp *rpages;
        unsigned long sb_bindex, id;
 
+       if (caa_unlikely(!len))
+               return -EINVAL;
        offset &= chanb->buf_size - 1;
        orig_offset = offset;
        id = bufb->buf_rsb.id;
@@ -420,8 +446,9 @@ int lib_ring_buffer_read_cstr(struct lttng_ust_lib_ring_buffer_backend *bufb, si
  *
  * Return the address where a given offset is located (for read).
  * Should be used to get the current subbuffer header pointer. Given we know
- * it's never on a page boundary, it's safe to write directly to this address,
- * as long as the write is never bigger than a page size.
+ * it's never on a page boundary, it's safe to read/write directly
+ * from/to this address, as long as the read/write is never bigger than
+ * a page size.
  */
 void *lib_ring_buffer_read_offset_address(struct lttng_ust_lib_ring_buffer_backend *bufb,
                                          size_t offset,