Fix mmap write() for large subbuffers and handle EINTR

With large subbuffer (packet) size, if write() returns before copying the entire packet for mmap buffers, the consumerd restarts the write infinitely, which is not good at all.

This affects both lttng-ust (in default mmap mode) and lttng-kernel (but only for mmap buffers, which is not the default).

This issue would show up with large subbuffer size.

We need to handle this case, as well as EINTR errors (which need to restart write).

Also fixing the return value of mmap read functions, which were returning the amount of data written by the last invocation of write() rather than the total number of bytes written. splice use had the same issue.

Also now consider a write() that returns more bytes than requested as an error.

Moreover, assigning error = ret after failed splice and write was a mistake: error is holding the actual error value. ret just holds -1.

Signed-off-by Mathieu Desnoyers <[email protected]>

--- diff --git a/src/common/kernel-consumer/kernel-consumer.c b/src/common/kernel-consumer/kernel-consumer.c index bbc31f8..739e06d 100644 --- a/src/common/kernel-consumer/kernel-consumer.c +++ b/src/common/kernel-consumer/kernel-consumer.c @@ -49,7 +49,7 @@ ssize_t lttng_kconsumer_on_read_subbuffer_mmap( struct lttng_consumer_stream *stream, unsigned long len) { unsigned long
mmap_offset; - ssize_t ret = 0; + ssize_t ret = 0, written = 0;
off_t orig_offset = stream->out_fd_offset; int fd = stream->wait_fd; int outfd = stream->out_fd; @@ -59,30 +59,40 @@ ssize_t lttng_kconsumer_on_read_subbuffer_mmap( if (ret != 0) {
errno = -ret; perror("kernctl_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; + }

(quoted diff) +1 -0

+		} 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; }

/* @@ -94,7 +104,7 @@ ssize_t lttng_kconsumer_on_read_subbuffer_splice( struct lttng_consumer_local_data *ctx, struct lttng_consumer_stream
*stream, unsigned long len) { - ssize_t ret = 0; + ssize_t ret = 0,
written = 0; loff_t offset = 0; off_t orig_offset = stream->out_fd_offset; int fd = stream->wait_fd; @@ -107,8 +117,11 @@ ssize_t lttng_kconsumer_on_read_subbuffer_splice( SPLICE_F_MOVE | SPLICE_F_MORE); DBG("splice chan to pipe ret %zd", ret); if (ret
< 0) { - errno = -ret; perror("Error in relay splice"); + if
(written == 0) { + written = ret; + } + ret = errno; goto
splice_error; }

(quoted diff) +0 -0

@@ -116,8 +129,18 @@ ssize_t

lttng_kconsumer_on_read_subbuffer_splice( SPLICE_F_MOVE | SPLICE_F_MORE); DBG("splice pipe to file %zd", ret); if (ret < 0)
{ - errno = -ret; perror("Error in file splice"); + if (written
== 0) { + written = ret; + } + ret = errno; + goto
splice_error; + } + if (ret > len) { + errno = EINVAL; +
perror("Wrote more data than requested"); + written += ret; +
ret = errno; goto splice_error; } len -= ret; @@ -125,6 +148,7 @@ ssize_t lttng_kconsumer_on_read_subbuffer_splice( 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);

(quoted diff) +0 -0

@@ -132,7 +156,7 @@ ssize_t

lttng_kconsumer_on_read_subbuffer_splice(

splice_error: /* send the appropriate error description to sessiond
*/ - switch(ret) { + switch (ret) { case EBADF:
lttng_consumer_send_error(ctx, CONSUMERD_SPLICE_EBADF); break; @@ -148,7 +172,7 @@ splice_error: }

end: - return ret; + return written; }

/* @@ -351,13 +375,14 @@ ssize_t lttng_kconsumer_read_subbuffer(struct lttng_consumer_stream *stream,

/* splice the subbuffer to the tracefile */ ret =
lttng_consumer_on_read_subbuffer_splice(ctx, stream, len); - if
(ret < 0) { + if (ret != len) { /* * display the error but
continue processing to try * to release the subbuffer */ ERR("Error splicing to tracefile"); } + break; case LTTNG_EVENT_MMAP: /* read the used subbuffer size */ @@ -369,7 +394,7 @@ ssize_t lttng_kconsumer_read_subbuffer(struct lttng_consumer_stream *stream, } /* 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 diff --git a/src/common/ust-consumer/ust-consumer.c b/src/common/ust-consumer/ust-consumer.c index 2b55fd4..a29eb58 100644 --- 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;

(quoted diff) +0 -0

@@ -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; - PERROR("Error in file write"); +
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;

(quoted diff) +1 -0

+		} 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; }

/* @@ -384,7 +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