[PATCH 1/6] pipeio: fix fwts_pipe_read return value when child produces no output

[Jeremy Kerr]

Currently, it's not possible to distinguish between a failure in
fwts_pipe_read(), and the child process outputting no data - in both
cases, NULL is returned.

This change moves the returned buffer to an output argument, with the
return value indicating errors.

Signed-off-by: Jeremy Kerr <jk at ozlabs.org>
---
 src/lib/include/fwts_pipeio.h |  2 +-
 src/lib/src/fwts_devicetree.c |  6 +++---
 src/lib/src/fwts_dump.c       |  2 +-
 src/lib/src/fwts_pipeio.c     | 21 +++++++++++----------
 4 files changed, 16 insertions(+), 15 deletions(-)

diff --git a/src/lib/include/fwts_pipeio.h b/src/lib/include/fwts_pipeio.h
index b014587..96952e0 100644
--- a/src/lib/include/fwts_pipeio.h
+++ b/src/lib/include/fwts_pipeio.h
@@ -31,7 +31,7 @@
 #define FWTS_EXEC_ERROR		(127)
 
 int   fwts_pipe_open(const char *command, pid_t *childpid);
-char *fwts_pipe_read(const int fd, ssize_t *length);
+int   fwts_pipe_read(const int fd, char **out_buf, ssize_t *out_len);
 int   fwts_pipe_close(const int fd, const pid_t pid);
 int   fwts_pipe_exec(const char *command, fwts_list **list, int *status);
 int   fwts_exec(const char *command, int *status);
diff --git a/src/lib/src/fwts_devicetree.c b/src/lib/src/fwts_devicetree.c
index 41cee54..b68a00e 100644
--- a/src/lib/src/fwts_devicetree.c
+++ b/src/lib/src/fwts_devicetree.c
@@ -46,15 +46,15 @@ int fwts_devicetree_read(fwts_framework *fwts)
 	}
 	free(command);
 
-	data = fwts_pipe_read(fd, &len);
-	if (data == NULL) {
+	rc = fwts_pipe_read(fd, &data, &len);
+	if (rc) {
 		fwts_pipe_close(fd, pid);
 		return FWTS_ERROR;
 	}
 
 	status = fwts_pipe_close(fd, pid);
 
-	if (!WIFEXITED(status) || WEXITSTATUS(status) != 0) {
+	if (!WIFEXITED(status) || WEXITSTATUS(status) != 0 || len == 0) {
 		fprintf(stderr, "Cannot read devicetree data: dtc failed\n");
 		return FWTS_ERROR;
 	}
diff --git a/src/lib/src/fwts_dump.c b/src/lib/src/fwts_dump.c
index b348d6f..edd2850 100644
--- a/src/lib/src/fwts_dump.c
+++ b/src/lib/src/fwts_dump.c
@@ -94,7 +94,7 @@ static int dump_exec(const char *filename, const char *command)
 	if ((fd = fwts_pipe_open(command, &pid)) < 0)
 		return FWTS_ERROR;
 
-	if ((data = fwts_pipe_read(fd, &len)) == NULL) {
+	if (fwts_pipe_read(fd, &data, &len) != 0) {
 		fwts_pipe_close(fd, pid);
 		return FWTS_ERROR;
 	}
diff --git a/src/lib/src/fwts_pipeio.c b/src/lib/src/fwts_pipeio.c
index 7dda976..75addc5 100644
--- a/src/lib/src/fwts_pipeio.c
+++ b/src/lib/src/fwts_pipeio.c
@@ -85,16 +85,16 @@ int fwts_pipe_open(const char *command, pid_t *childpid)
 
 /*
  *  fwts_pipe_read()
- *	read output from fwts_pipe_open(), *length is
- *	set to the number of chars read and we return
- *	a buffer of read data.
+ *	read output from fwts_pipe_open(), *out_buf is populated with returned
+ *	data (allocated, must be free()-ed after use), and length in *out_len.
+ *	Returns non-zero on failure.
  */
-char *fwts_pipe_read(const int fd, ssize_t *length)
+int fwts_pipe_read(const int fd, char **out_buf, ssize_t *out_len)
 {
 	char *ptr = NULL;
 	char buffer[8192];
 	ssize_t size = 0;
-	*length = 0;
+	*out_len = 0;
 
 	ptr = NULL;
 
@@ -107,22 +107,23 @@ char *fwts_pipe_read(const int fd, ssize_t *length)
 		if (n < 0) {
 			if (errno != EINTR && errno != EAGAIN) {
 				free(ptr);
-				return NULL;
+				return -1;
 			}
 			continue;
 		}
 
 		if ((tmp = realloc(ptr, size + n + 1)) == NULL) {
 			free(ptr);
-			return NULL;
+			return -1;
 		}
 		ptr = tmp;
 		memcpy(ptr + size, buffer, n);
 		size += n;
 		*(ptr+size) = 0;
 	}
-	*length = size;
-	return ptr;
+	*out_len = size;
+	*out_buf = ptr;
+	return 0;
 }
 
 /*
@@ -162,7 +163,7 @@ int fwts_pipe_exec(const char *command, fwts_list **list, int *status)
 	if ((fd = fwts_pipe_open(command, &pid)) < 0)
 		return FWTS_ERROR;
 
-	text = fwts_pipe_read(fd, &len);
+	fwts_pipe_read(fd, &text, &len);
 	*list = fwts_list_from_text(text);
 	free(text);
 
-- 
2.5.0