+ CHAN_WARN_ON(chanb, (offset & (chanb->buf_size - 1)) + len > chanb->buf_size);
+ backend_pages = lib_ring_buffer_get_backend_pages_from_ctx(config, ctx);
+ if (caa_unlikely(!backend_pages)) {
+ if (lib_ring_buffer_backend_get_pages(config, ctx, &backend_pages))
+ return;
+ }
+ p = shmp_index(handle, backend_pages->p, offset & (chanb->subbuf_size - 1));
+ if (caa_unlikely(!p))
+ return;
+ lib_ring_buffer_do_copy(config, p, src, len);
+ ctx->buf_offset += len;
+}
+
+/*
+ * Copy up to @len string bytes from @src to @dest. Stop whenever a NULL
+ * terminating character is found in @src. Returns the number of bytes
+ * copied. Does *not* terminate @dest with NULL terminating character.
+ */
+static inline __attribute__((always_inline))
+size_t lib_ring_buffer_do_strcpy(const struct lttng_ust_lib_ring_buffer_config *config,
+ char *dest, const char *src, size_t len)
+{
+ size_t count;
+
+ for (count = 0; count < len; count++) {
+ char c;
+
+ /*
+ * Only read source character once, in case it is
+ * modified concurrently.
+ */
+ c = CMM_LOAD_SHARED(src[count]);
+ if (!c)
+ break;
+ lib_ring_buffer_do_copy(config, &dest[count], &c, 1);
+ }
+ return count;
+}
+
+/**
+ * lib_ring_buffer_strcpy - write string data to a buffer backend
+ * @config : ring buffer instance configuration
+ * @ctx: ring buffer context. (input arguments only)
+ * @src : source pointer to copy from
+ * @len : length of data to copy
+ * @pad : character to use for padding
+ *
+ * This function copies @len - 1 bytes of string data from a source
+ * pointer to a buffer backend, followed by a terminating '\0'
+ * character, at the current context offset. This is more or less a
+ * buffer backend-specific strncpy() operation. If a terminating '\0'
+ * character is found in @src before @len - 1 characters are copied, pad
+ * the buffer with @pad characters (e.g. '#').
+ */
+static inline __attribute__((always_inline))
+void lib_ring_buffer_strcpy(const struct lttng_ust_lib_ring_buffer_config *config,
+ struct lttng_ust_lib_ring_buffer_ctx *ctx,
+ const char *src, size_t len, int pad)
+{
+ struct channel_backend *chanb = &ctx->chan->backend;
+ struct lttng_ust_shm_handle *handle = ctx->handle;
+ size_t count;
+ size_t offset = ctx->buf_offset;
+ struct lttng_ust_lib_ring_buffer_backend_pages *backend_pages;
+ void *p;
+
+ if (caa_unlikely(!len))
+ return;
+ /*
+ * Underlying layer should never ask for writes across
+ * subbuffers.
+ */
+ CHAN_WARN_ON(chanb, (offset & (chanb->buf_size - 1)) + len > chanb->buf_size);
+ backend_pages = lib_ring_buffer_get_backend_pages_from_ctx(config, ctx);
+ if (caa_unlikely(!backend_pages)) {
+ if (lib_ring_buffer_backend_get_pages(config, ctx, &backend_pages))
+ return;
+ }
+ p = shmp_index(handle, backend_pages->p, offset & (chanb->subbuf_size - 1));
+ if (caa_unlikely(!p))
+ return;
+
+ count = lib_ring_buffer_do_strcpy(config, p, src, len - 1);
+ offset += count;
+ /* Padding */
+ if (caa_unlikely(count < len - 1)) {
+ size_t pad_len = len - 1 - count;
+
+ p = shmp_index(handle, backend_pages->p, offset & (chanb->subbuf_size - 1));
+ if (caa_unlikely(!p))
+ return;
+ lib_ring_buffer_do_memset(p, pad, pad_len);
+ offset += pad_len;
+ }
+ /* Final '\0' */
+ p = shmp_index(handle, backend_pages->p, offset & (chanb->subbuf_size - 1));
+ if (caa_unlikely(!p))
+ return;
+ lib_ring_buffer_do_memset(p, '\0', 1);