Fix: mmap write() for large subbuffers and handle EINTR (v2)

[lttng-tools.git] / src / common / ust-consumer / ust-consumer.c

diff --git a/src/common/ust-consumer/ust-consumer.c b/src/common/ust-consumer/ust-consumer.c
index bfdb7e968fe9aa77ba9ad922e8fb6bf8748f4353..47c0d460ffb60cc612d9806325602c6eac459023 100644 (file)
--- a/src/common/ust-consumer/ust-consumer.c
+++ b/src/common/ust-consumer/ust-consumer.c
@@ -49,7 +49,7 @@ ssize_t lttng_ustconsumer_on_read_subbuffer_mmap(
                struct lttng_consumer_stream *stream, unsigned long len)
 {
        unsigned long mmap_offset;
-       long ret = 0;
+       long ret = 0, written = 0;
        off_t orig_offset = stream->out_fd_offset;
        int outfd = stream->out_fd;
 
@@ -59,29 +59,39 @@ ssize_t lttng_ustconsumer_on_read_subbuffer_mmap(
        if (ret != 0) {
                errno = -ret;
                PERROR("ustctl_get_mmap_read_offset");
+               written = ret;
                goto end;
        }
        while (len > 0) {
                ret = write(outfd, stream->mmap_base + mmap_offset, len);
-               if (ret >= len) {
-                       len = 0;
-               } else if (ret < 0) {
-                       errno = -ret;
+               if (ret < 0) {
+                       if (errno == EINTR) {
+                               /* restart the interrupted system call */
+                               continue;
+                       } else {
+                               PERROR("Error in file write");
+                               if (written == 0) {
+                                       written = ret;
+                               }
+                               goto end;
+                       }
+               } else if (ret > len) {
                        PERROR("Error in file write");
+                       written += ret;
                        goto end;
+               } else {
+                       len -= ret;
+                       mmap_offset += ret;
                }
                /* This won't block, but will start writeout asynchronously */
                lttng_sync_file_range(outfd, stream->out_fd_offset, ret,
                                SYNC_FILE_RANGE_WRITE);
                stream->out_fd_offset += ret;
+               written += ret;
        }
-
        lttng_consumer_sync_trace_file(stream, orig_offset);
-
-       goto end;
-
 end:
-       return ret;
+       return written;
 }
 
 /*
@@ -257,11 +267,20 @@ int lttng_ustconsumer_recv_cmd(struct lttng_consumer_local_data *ctx,
                break;
        }
 end:
-       /* signal the poll thread */
-       ret = write(ctx->consumer_poll_pipe[1], "4", 1);
-       if (ret < 0) {
-               PERROR("write consumer poll");
-       }
+       /*
+        * Wake-up the other end by writing a null byte in the pipe
+        * (non-blocking). Important note: Because writing into the
+        * pipe is non-blocking (and therefore we allow dropping wakeup
+        * data, as long as there is wakeup data present in the pipe
+        * buffer to wake up the other end), the other end should
+        * perform the following sequence for waiting:
+        * 1) empty the pipe (reads).
+        * 2) perform update operation.
+        * 3) wait on the pipe (poll).
+        */
+       do {
+               ret = write(ctx->consumer_poll_pipe[1], "", 1);
+       } while (ret == -1UL && errno == EINTR);
 end_nosignal:
        return 0;
 }
@@ -375,7 +394,7 @@ int lttng_ustconsumer_read_subbuffer(struct lttng_consumer_stream *stream,
        assert(err == 0);
        /* write the subbuffer to the tracefile */
        ret = lttng_consumer_on_read_subbuffer_mmap(ctx, stream, len);
-       if (ret < 0) {
+       if (ret != len) {
                /*
                 * display the error but continue processing to try
                 * to release the subbuffer