fix several problems in dd

dd.c

@@ -33,7 +33,6 @@ struct dd_config {
 	off_t fsize;
 	blksize_t bs;
 	char quiet, nosync, direct;
-	int saved_errno;
 	time_t t_start, t_end;
 };
 
@@ -52,20 +51,17 @@ prepare_copy(struct dd_config *ddc, int *ifd, int *ofd)
 		flo |= O_DIRECT;
 	}
 
-	if (stat(ddc->in, &st) < 0) {
-		ddc->saved_errno = errno;
-		return -1;
-	}
-
 	euid = geteuid();
 
 	if (!euid || st.st_uid == euid)
 		fli |= O_NOATIME;
 
-	if ((*ifd = open(ddc->in, fli)) < 0) {
+	if (!ddc->in) *ifd = 0;
-		ddc->saved_errno = errno;
+	else if ((*ifd = open(ddc->in, fli)) < 0)
+		return -1;
+
+	if (fstat(*ifd, &st) < 0)
 		return -1;
-	}
 
 	ddc->fsize = st.st_size;
 
@@ -90,14 +86,11 @@ prepare_copy(struct dd_config *ddc, int *ifd, int *ofd)
 	if (!S_ISREG(st.st_mode)) {
 		if (S_ISBLK(st.st_mode)) {
 			if (ioctl(*ifd, BLKGETSIZE64, &ddc->fsize) < 0) {
-				ddc->saved_errno = errno;
 				close(*ifd);
 				return -1;
 			}
 		} else {
 			ddc->fsize = (off_t)-1;
-			if (ddc->count)
-				ddc->fsize = ddc->count*ddc->bs;
 		}
 	}
 
@@ -107,7 +100,7 @@ prepare_copy(struct dd_config *ddc, int *ifd, int *ofd)
 
 	/* skip more bytes than are inside source file? */
 	if (ddc->fsize != (off_t)-1 && ddc->skip >= (uint64_t)ddc->fsize) {
-		ddc->saved_errno = EINVAL;
+		errno = EINVAL;
 		close(*ifd);
 		return -1;
 	}
@@ -115,14 +108,23 @@ prepare_copy(struct dd_config *ddc, int *ifd, int *ofd)
 	if (!ddc->seek)
 		flo |= O_CREAT|O_TRUNC;
 
-	if ((*ofd = open(ddc->out, flo, st.st_mode)) < 0) {
+	if (!ddc->out) *ofd = 1;
-		ddc->saved_errno = errno;
+	else if ((*ofd = open(ddc->out, flo, st.st_mode)) < 0) {
 		close(*ifd);
 		return -1;
 	}
 
-	lseek(*ifd, ddc->skip, SEEK_SET);
+	if (lseek(*ifd, ddc->skip, SEEK_CUR) < 0) {
-	lseek(*ofd, ddc->seek, SEEK_SET);
+		char buffer[ddc->bs];
+		for (uint64_t i = 0; i < ddc->skip; i += ddc->bs) {
+			if (read(*ifd, &buffer, ddc->bs) < 0) {
+				errno = EINVAL;
+				close(*ifd);
+				return -1;
+			}
+		}
+	}
+	lseek(*ofd, ddc->seek, SEEK_CUR);
 	posix_fadvise(*ifd, ddc->skip, 0, POSIX_FADV_SEQUENTIAL);
 	posix_fadvise(*ofd, 0, 0, POSIX_FADV_DONTNEED);
 
@@ -147,7 +149,6 @@ copy_splice(struct dd_config *ddc)
 	if (prepare_copy(ddc, &ifd, &ofd) < 0)
 		return -1;
 	if (pipe(p) < 0) {
-		ddc->saved_errno = errno;
 		close(ifd); close(ofd);
 		close(p[0]); close(p[1]);
 		return -1;
@@ -165,24 +166,18 @@ copy_splice(struct dd_config *ddc)
 		FD_SET(ifd, &rfd);
 		FD_SET(ofd, &wfd);
 		r = select(ifd > ofd ? ifd + 1 : ofd + 1, &rfd, &wfd, NULL, NULL);
-		if (r < 0) {
+		if (r < 0)
-			ddc->saved_errno = errno;
 			break;
-		}
 		if (FD_ISSET(ifd, &rfd) == 1 && FD_ISSET(ofd, &wfd) == 1) {
 			if (n > ddc->count - ddc->b_out)
 				n = ddc->count - ddc->b_out;
 			r = splice(ifd, NULL, p[1], NULL, n, SPLICE_F_MORE);
-			if (r <= 0) {
+			if (r <= 0)
-				ddc->saved_errno = errno;
 				break;
-			}
 			++ddc->rec_in;
 			r = splice(p[0], NULL, ofd, NULL, r, SPLICE_F_MORE);
-			if (r <= 0) {
+			if (r <= 0)
-				ddc->saved_errno = errno;
 				break;
-			}
 			ddc->b_out += r;
 			++ddc->rec_out;
 		}
@@ -252,16 +247,16 @@ main(int argc, char *argv[])
 	argv0 = argv[0];
 	memset(&config, 0, sizeof(config));
 	config.bs = 1<<16;
-	config.in = "/dev/stdin";
+	config.in = NULL;
-	config.out = "/dev/stdout";
+	config.out = NULL;
 
 	/* emulate 'dd' argument parsing */
 	for (i = 1; i < argc; ++i) {
 		memset(buf, 0, sizeof(buf));
-		if (sscanf(argv[i], "if=%1023s", buf) == 1)
+		if (strncmp(argv[i], "if=", 3) == 0)
-			config.in = strdup(buf);
+			config.in = argv[i]+3;
-		else if (sscanf(argv[i], "of=%1023s", buf) == 1)
+		else if (strncmp(argv[i], "of=", 3) == 0)
-			config.out = strdup(buf);
+			config.out = argv[i]+3;
 		else if (sscanf(argv[i], "skip=%1023s", buf) == 1)
 			config.skip = estrtoul(buf, 0);
 		else if (sscanf(argv[i], "seek=%1023s", buf) == 1)
@@ -282,9 +277,6 @@ main(int argc, char *argv[])
 			usage();
 	}
 
-	if (!config.in || !config.out)
-		usage();
-
 	signal(SIGPIPE, SIG_IGN);
 	signal(SIGINT, sig_int);
 
@@ -294,5 +286,5 @@ main(int argc, char *argv[])
 
 	if (config.nosync == 0)
 		sync();
-	return config.saved_errno;
+	return errno;
 }