lib/process: Don't abort stdout reads on EINTR

If our read() of the process stdout pipe fails with EINTR (eg, if we
receive a SIGCHLD because the process exited), then
process_read_stdout_once will return a non-zero exit code, and we'll
abort any further stdout collection.

Instead, we should check for EINTR, and allow the reads to continue.

This change normalises the return value from process_read_stdout_once to
return positive on success, negative on failure, and zero on competion.
We use a positive return value for the non-error EINTR case.

Also, add a pb_log if the read fails for non-EINTR reasons.

Signed-off-by: Jeremy Kerr <jk@ozlabs.org>

1 files changed, 15 insertions, 3 deletions

diff --git a/lib/process/process.c b/lib/process/process.c
index 86c7fbb..081a48c 100644
--- a/lib/process/process.c
+++ b/lib/process/process.c
@@ -61,7 +61,13 @@ static struct process_info *get_info(struct process *process)
 }
 
 /* Read as much as possible into the currently-allocated stdout buffer, and
- * possibly realloc it for the next read */
+ * possibly realloc it for the next read
+ *
+ * Returns:
+ *  > 0 on success (even though no bytes may have been read)
+ *    0 on EOF (no error, but no more reads can be performed)
+ *  < 0 on error
+ **/
 static int process_read_stdout_once(struct process_info *procinfo)
 {
 	struct process *process = &procinfo->process;
@@ -74,8 +80,14 @@ static int process_read_stdout_once(struct process_info *procinfo)
 	max_len =  procinfo->stdout_buf_len - process->stdout_len - 1;
 
 	rc = read(fd, process->stdout_buf + process->stdout_len, max_len);
-	if (rc <= 0)
+	if (rc == 0)
+		return 0;
+	if (rc < 0) {
+		if (errno == EINTR)
+			return 1;
+		pb_log("%s: read failed: %s\n", __func__, strerror(errno));
 		return rc;
+	}
 
 	process->stdout_len += rc;
 	if (process->stdout_len == procinfo->stdout_buf_len - 1) {
@@ -85,7 +97,7 @@ static int process_read_stdout_once(struct process_info *procinfo)
 				procinfo->stdout_buf_len);
 	}
 
-	return rc;
+	return 1;
 }
 
 static int process_setup_stdout_pipe(struct process_info *procinfo)