+/*
+ * on_read_subbuffer_mmap
+ *
+ * mmap the ring buffer, read it and write the data to the tracefile.
+ * Returns the number of bytes written
+ */
+static int on_read_subbuffer_mmap(struct ltt_kconsumerd_fd *kconsumerd_fd,
+ unsigned long len)
+{
+ unsigned long mmap_len;
+ unsigned long mmap_offset;
+ unsigned long padded_len;
+ unsigned long padding_len;
+ char *mmap_base;
+ char *padding = NULL;
+ long ret = 0;
+ off_t orig_offset = kconsumerd_fd->out_fd_offset;
+ int fd = kconsumerd_fd->consumerd_fd;
+ int outfd = kconsumerd_fd->out_fd;
+
+ /* get the padded subbuffer size to know the padding required */
+ ret = kernctl_get_padded_subbuf_size(fd, &padded_len);
+ if (ret != 0) {
+ ret = errno;
+ perror("kernctl_get_padded_subbuf_size");
+ goto end;
+ }
+ padding_len = padded_len - len;
+ padding = malloc(padding_len * sizeof(char));
+ memset(padding, '\0', padding_len);
+
+ /* get the len of the mmap region */
+ ret = kernctl_get_mmap_len(fd, &mmap_len);
+ if (ret != 0) {
+ ret = errno;
+ perror("kernctl_get_mmap_len");
+ goto end;
+ }
+
+ /* get the offset inside the fd to mmap */
+ ret = kernctl_get_mmap_read_offset(fd, &mmap_offset);
+ if (ret != 0) {
+ ret = errno;
+ perror("kernctl_get_mmap_read_offset");
+ goto end;
+ }
+
+ mmap_base = mmap(NULL, mmap_len, PROT_READ, MAP_PRIVATE, fd, mmap_offset);
+ if (mmap_base == MAP_FAILED) {
+ perror("Error mmaping");
+ ret = -1;
+ goto end;
+ }
+
+ while (len > 0) {
+ ret = write(outfd, mmap_base, len);
+ if (ret >= len) {
+ len = 0;
+ } else if (ret < 0) {
+ ret = errno;
+ perror("Error in file write");
+ goto end;
+ }
+ /* This won't block, but will start writeout asynchronously */
+ sync_file_range(outfd, kconsumerd_fd->out_fd_offset, ret,
+ SYNC_FILE_RANGE_WRITE);
+ kconsumerd_fd->out_fd_offset += ret;
+ }
+
+ /* once all the data is written, write the padding to disk */
+ ret = write(outfd, padding, padding_len);
+ if (ret < 0) {
+ ret = errno;
+ perror("Error writing padding to file");
+ goto end;
+ }
+
+ /*
+ * This does a blocking write-and-wait on any page that belongs to the
+ * subbuffer prior to the one we just wrote.
+ * Don't care about error values, as these are just hints and ways to
+ * limit the amount of page cache used.
+ */
+ if (orig_offset >= kconsumerd_fd->max_sb_size) {
+ sync_file_range(outfd, orig_offset - kconsumerd_fd->max_sb_size,
+ kconsumerd_fd->max_sb_size,
+ SYNC_FILE_RANGE_WAIT_BEFORE
+ | SYNC_FILE_RANGE_WRITE
+ | SYNC_FILE_RANGE_WAIT_AFTER);
+ /*
+ * Give hints to the kernel about how we access the file:
+ * POSIX_FADV_DONTNEED : we won't re-access data in a near
+ * future after we write it.
+ * We need to call fadvise again after the file grows because
+ * the kernel does not seem to apply fadvise to non-existing
+ * parts of the file.
+ * Call fadvise _after_ having waited for the page writeback to
+ * complete because the dirty page writeback semantic is not
+ * well defined. So it can be expected to lead to lower
+ * throughput in streaming.
+ */
+ posix_fadvise(outfd, orig_offset - kconsumerd_fd->max_sb_size,
+ kconsumerd_fd->max_sb_size, POSIX_FADV_DONTNEED);
+ }
+ goto end;
+
+end:
+ if (padding != NULL) {
+ free(padding);
+ }
+ return ret;
+}
+
projects / lttng-tools.git / blobdiff