tar: conditionally don't wait for vforked child to exec, as it always

works right on Linux, and anyway mayresult only on less-than-clear error
message only, it will not cause tar to misbehave.

function                                             old     new   delta
open_transformer                                      98      80     -18
writeTarFile                                         714     547    -167
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 0/2 up/down: 0/-185)           Total: -185 bytes
   text    data     bss     dec     hex filename
 770651    1051   10764  782466   bf082 busybox_old
 770463    1051   10764  782278   befc6 busybox_unstripped

1 files changed, 47 insertions, 35 deletions

diff --git a/archival/tar.c b/archival/tar.c
index 9bf9058..f0d3971 100644
--- a/archival/tar.c
+++ b/archival/tar.c
@@ -106,7 +106,7 @@ enum TarFileType {
 typedef enum TarFileType TarFileType;
 
 /* Might be faster (and bigger) if the dev/ino were stored in numeric order;) */
-static void addHardLinkInfo(HardLinkInfo ** hlInfoHeadPtr,
+static void addHardLinkInfo(HardLinkInfo **hlInfoHeadPtr,
 					struct stat *statbuf,
 					const char *fileName)
 {
@@ -122,7 +122,7 @@ static void addHardLinkInfo(HardLinkInfo ** hlInfoHeadPtr,
 	strcpy(hlInfo->name, fileName);
 }
 
-static void freeHardLinkInfo(HardLinkInfo ** hlInfoHeadPtr)
+static void freeHardLinkInfo(HardLinkInfo **hlInfoHeadPtr)
 {
 	HardLinkInfo *hlInfo;
 	HardLinkInfo *hlInfoNext;
@@ -139,7 +139,7 @@ static void freeHardLinkInfo(HardLinkInfo ** hlInfoHeadPtr)
 }
 
 /* Might be faster (and bigger) if the dev/ino were stored in numeric order;) */
-static HardLinkInfo *findHardLinkInfo(HardLinkInfo * hlInfo, struct stat *statbuf)
+static HardLinkInfo *findHardLinkInfo(HardLinkInfo *hlInfo, struct stat *statbuf)
 {
 	while (hlInfo) {
 		if ((statbuf->st_ino == hlInfo->ino) && (statbuf->st_dev == hlInfo->dev))
@@ -504,13 +504,21 @@ static int writeTarFile(const int tar_fd, const int verboseFlag,
 		bb_perror_msg_and_die("cannot stat tar file");
 
 	if ((ENABLE_FEATURE_TAR_GZIP || ENABLE_FEATURE_TAR_BZIP2) && gzip) {
-		int gzipDataPipe[2] = { -1, -1 };
-		int gzipStatusPipe[2] = { -1, -1 };
+// On Linux, vfork never unpauses parent early, although standard
+// allows for that. Do we want to waste bytes checking for it?
+#define WAIT_FOR_CHILD 0
+
 		volatile int vfork_exec_errno = 0;
+#if WAIT_FOR_CHILD
+		struct { int rd; int wr; } gzipStatusPipe;
+#endif
+		struct { int rd; int wr; } gzipDataPipe;
 		const char *zip_exec = (gzip == 1) ? "gzip" : "bzip2";
 
-		xpipe(gzipDataPipe);
-		xpipe(gzipStatusPipe);
+		xpipe(&gzipDataPipe.rd);
+#if WAIT_FOR_CHILD
+		xpipe(&gzipStatusPipe.rd);
+#endif
 
 		signal(SIGPIPE, SIG_IGN); /* we only want EPIPE on errors */
 
@@ -522,41 +530,45 @@ static int writeTarFile(const int tar_fd, const int verboseFlag,
 #endif
 
 		gzipPid = vfork();
+		if (gzipPid < 0)
+			bb_perror_msg_and_die("vfork gzip");
 
 		if (gzipPid == 0) {
-			dup2(gzipDataPipe[0], 0);
-			close(gzipDataPipe[1]);
-
-			dup2(tbInfo.tarFd, 1);
-
-			close(gzipStatusPipe[0]);
-			fcntl(gzipStatusPipe[1], F_SETFD, FD_CLOEXEC);	/* close on exec shows success */
-
+			/* child */
+			xmove_fd(tbInfo.tarFd, 1);
+			xmove_fd(gzipDataPipe.rd, 0);
+			close(gzipDataPipe.wr);
+#if WAIT_FOR_CHILD
+			close(gzipStatusPipe.rd);
+			fcntl(gzipStatusPipe.wr, F_SETFD, FD_CLOEXEC);
+#endif
+			/* exec gzip/bzip2 program/applet */
 			BB_EXECLP(zip_exec, zip_exec, "-f", NULL);
 			vfork_exec_errno = errno;
+			_exit(1);
+		}
 
-			close(gzipStatusPipe[1]);
-			exit(-1);
-		} else if (gzipPid > 0) {
-			close(gzipDataPipe[0]);
-			close(gzipStatusPipe[1]);
-
-			while (1) {
-				char buf;
-
-				int n = full_read(gzipStatusPipe[0], &buf, 1);
+		/* parent */
+		xmove_fd(gzipDataPipe.wr, tbInfo.tarFd);
+		close(gzipDataPipe.rd);
+#if WAIT_FOR_CHILD
+		close(gzipStatusPipe.wr);
+		while (1) {
+			char buf;
+			int n;
 
-				if (n == 0 && vfork_exec_errno != 0) {
-					errno = vfork_exec_errno;
-					bb_perror_msg_and_die("cannot exec %s", zip_exec);
-				} else if ((n < 0) && (errno == EAGAIN || errno == EINTR))
-					continue;	/* try it again */
-				break;
-			}
-			close(gzipStatusPipe[0]);
+			/* Wait until child execs (or fails to) */
+			n = full_read(gzipStatusPipe.rd, &buf, 1);
+			if ((n < 0) && (/*errno == EAGAIN ||*/ errno == EINTR))
+				continue;	/* try it again */
 
-			tbInfo.tarFd = gzipDataPipe[1];
-		} else bb_perror_msg_and_die("vfork gzip");
+		}
+		close(gzipStatusPipe.rd);
+#endif
+		if (vfork_exec_errno) {
+			errno = vfork_exec_errno;
+			bb_perror_msg_and_die("cannot exec %s", zip_exec);
+		}
 	}
 
 	tbInfo.excludeList = exclude;