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>

2 files changed, 58 insertions, 0 deletions

diff --git a/test/lib/Makefile.am b/test/lib/Makefile.am
index ed570af..23bee36 100644
--- a/test/lib/Makefile.am
+++ b/test/lib/Makefile.am
@@ -32,6 +32,7 @@ check_PROGRAMS = list-test \
 	test-process-async-stdout \
 	test-process-parent-stdout \
 	test-process-both \
+	test-process-stdout-eintr \
 	test-fold
 
 TESTS = $(check_PROGRAMS)
diff --git a/test/lib/test-process-stdout-eintr.c b/test/lib/test-process-stdout-eintr.c
new file mode 100644
index 0000000..b62d570
--- /dev/null
+++ b/test/lib/test-process-stdout-eintr.c
@@ -0,0 +1,57 @@
+
+#include <stdlib.h>
+#include <string.h>
+#include <assert.h>
+#include <signal.h>
+
+#include <process/process.h>
+#include <waiter/waiter.h>
+#include <talloc/talloc.h>
+
+static int do_child(int ppid)
+{
+	sleep(1);
+	kill(ppid, SIGCHLD);
+	printf("forty two\n");
+	return 42;
+}
+
+int main(int argc, char **argv)
+{
+	struct waitset *waitset;
+	struct process *process;
+	const char *child_argv[3];
+	void *ctx;
+
+	if (argc == 3 && !strcmp(argv[1], "child"))
+		return do_child(atoi(argv[2]));
+
+	ctx = talloc_new(NULL);
+
+	waitset = waitset_create(ctx);
+
+	process_init(ctx, waitset, false);
+
+	child_argv[0] = argv[0];
+	child_argv[1] = "child";
+	child_argv[2] = talloc_asprintf(ctx, "%d", getpid());
+	child_argv[3] = NULL;
+
+	process = process_create(ctx);
+	process->path = child_argv[0];
+	process->argv = child_argv;
+	process->keep_stdout = true;
+
+	process_run_sync(process);
+
+	assert(WIFEXITED(process->exit_status));
+	assert(WEXITSTATUS(process->exit_status) == 42);
+
+	assert(process->stdout_len == strlen("forty two\n"));
+	assert(!memcmp(process->stdout_buf, "forty two\n",
+				process->stdout_len));
+
+	talloc_free(ctx);
+
+	return EXIT_SUCCESS;
+}