[ccan] [PATCH v3 2/13] configurator: Reimplement run using popen

[Kevin Locke]

On Tue, 2016-09-27 at 14:52 +1000, David Gibson wrote:
> On Thu, Sep 22, 2016 at 09:33:05PM -0600, Kevin Locke wrote:
>> - Create fread_noeintr to avoid EINTR in fread without reading any data.
>> - Handle short reads from fread.  This can happen with non-conformant
>>   libc or if EINTR occurs after reading some data.
> 
> Hrm.  Have you actually confirmed this problem with EINTR?  My
> previous objections to not handling short read were based entirely on
> not realizing that fread() wasn't supposed to do that, rather than
> thinking of some edge case you hadn't.
> 
> Unless we have a confirmed case where fread() can give a short read
> that won't have feof() or ferror() set afterwards, I'm inclined to go
> back to your initial implementation.

Nope, I was just being overly cautious.  Sounds good to me.  Below is
an updated patch which is the same as v1 but with the addition of the
#define for _POSIX_C_SOURCE to get pclose, popen, and strdup.

-8<--------------------------------------------------------------------
Rather than using fork+pipe+system+waitpid, most of which are only
available on POSIX-like systems, use popen which is also available on
Windows (under the name _popen).

Changes since v1:
- Create fread_noeintr to avoid EINTR in fread without reading any data.
- Handle short reads from fread.  This can happen with non-conformant
  libc or if EINTR occurs after reading some data.
- Define _POSIX_C_SOURCE for popen/pclose with strict implementations
  which require it (e.g. gcc with -std=c11).

Changes since v2:
- Revert fread_noeintr and short read changes in v1 as unnecessary.

Signed-off-by: Kevin Locke <kevin at kevinlocke.name>
---
 tools/configurator/configurator.c | 79 +++++++++++++++------------------------
 1 file changed, 31 insertions(+), 48 deletions(-)

diff --git a/tools/configurator/configurator.c b/tools/configurator/configurator.c
index c7577c0..2ad3fff 100644
--- a/tools/configurator/configurator.c
+++ b/tools/configurator/configurator.c
@@ -21,17 +21,19 @@
  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  * THE SOFTWARE.
  */
+#define _POSIX_C_SOURCE 200809L                /* For pclose, popen, strdup */
+
 #include <stdio.h>
 #include <stdbool.h>
 #include <stdlib.h>
-#include <unistd.h>
 #include <err.h>
-#include <sys/types.h>
-#include <sys/wait.h>
-#include <sys/stat.h>
-#include <fcntl.h>
 #include <string.h>

+#ifdef _MSC_VER
+#define popen _popen
+#define pclose _pclose
+#endif
+
 #define DEFAULT_COMPILER "cc"
 #define DEFAULT_FLAGS "-g3 -ggdb -Wall -Wundef -Wmissing-prototypes -Wmissing-declarations -Wstrict-prototypes -Wold-style-definition"

@@ -375,20 +377,19 @@ static struct test tests[] = {
 	},
 };

-static char *grab_fd(int fd)
+static char *grab_stream(FILE *file)
 {
-	int ret;
-	size_t max, size = 0;
+	size_t max, ret, size = 0;
 	char *buffer;

-	max = 16384;
-	buffer = malloc(max+1);
-	while ((ret = read(fd, buffer + size, max - size)) > 0) {
+	max = BUFSIZ;
+	buffer = malloc(max);
+	while ((ret = fread(buffer+size, 1, max - size, file)) == max - size) {
 		size += ret;
-		if (size == max)
-			buffer = realloc(buffer, max *= 2);
+		buffer = realloc(buffer, max *= 2);
 	}
-	if (ret < 0)
+	size += ret;
+	if (ferror(file))
 		err(1, "reading from command");
 	buffer[size] = '\0';
 	return buffer;
@@ -396,43 +397,25 @@ static char *grab_fd(int fd)

 static char *run(const char *cmd, int *exitstatus)
 {
-	pid_t pid;
-	int p[2];
+	static const char redir[] = " 2>&1";
+	size_t cmdlen;
+	char *cmdredir;
+	FILE *cmdout;
 	char *ret;
-	int status;

-	if (pipe(p) != 0)
-		err(1, "creating pipe");
-
-	pid = fork();
-	if (pid == -1)
-		err(1, "forking");
-
-	if (pid == 0) {
-		if (dup2(p[1], STDOUT_FILENO) != STDOUT_FILENO
-		    || dup2(p[1], STDERR_FILENO) != STDERR_FILENO
-		    || close(p[0]) != 0
-		    || close(STDIN_FILENO) != 0
-		    || open("/dev/null", O_RDONLY) != STDIN_FILENO)
-			exit(128);
-
-		status = system(cmd);
-		if (WIFEXITED(status))
-			exit(WEXITSTATUS(status));
-		/* Here's a hint... */
-		exit(128 + WTERMSIG(status));
-	}
+	cmdlen = strlen(cmd);
+	cmdredir = malloc(cmdlen + sizeof(redir));
+	memcpy(cmdredir, cmd, cmdlen);
+	memcpy(cmdredir + cmdlen, redir, sizeof(redir));
+
+	cmdout = popen(cmdredir, "r");
+	if (!cmdout)
+		err(1, "popen \"%s\"", cmdredir);
+
+	free(cmdredir);

-	close(p[1]);
-	ret = grab_fd(p[0]);
-	/* This shouldn't fail... */
-	if (waitpid(pid, &status, 0) != pid)
-		err(1, "Failed to wait for child");
-	close(p[0]);
-	if (WIFEXITED(status))
-		*exitstatus = WEXITSTATUS(status);
-	else
-		*exitstatus = -WTERMSIG(status);
+	ret = grab_stream(cmdout);
+	*exitstatus = pclose(cmdout);
 	return ret;
 }

--
2.9.3