From 9870b77f9000c55bbe507bbb11d6d20fac2e8da0 Mon Sep 17 00:00:00 2001
From: Tavian Barnes <tavianator@tavianator.com>
Date: Thu, 15 Apr 2021 14:34:55 -0400
Subject: util: Tweak the safe read/write functions

---
 bar.c   |  2 +-
 spawn.c |  8 ++++----
 util.c  | 71 ++++++++++++++++++++++++++++-------------------------------------
 util.h  | 27 ++++++++++++-------------
 4 files changed, 49 insertions(+), 59 deletions(-)

diff --git a/bar.c b/bar.c
index 33127f8..31734ac 100644
--- a/bar.c
+++ b/bar.c
@@ -58,7 +58,7 @@ static int bfs_bar_getsize(struct bfs_bar *bar) {
 /** Async Signal Safe puts(). */
 static int ass_puts(int fd, const char *str) {
 	size_t len = strlen(str);
-	return safe_write_all(fd, str, len) == (ssize_t)len ? 0 : -1;
+	return xwrite(fd, str, len) == len ? 0 : -1;
 }
 
 /** Number of decimal digits needed for terminal sizes. */
diff --git a/spawn.c b/spawn.c
index 0a260dc..094214b 100644
--- a/spawn.c
+++ b/spawn.c
@@ -189,9 +189,9 @@ static void bfs_spawn_exec(const char *exe, const struct bfs_spawn *ctx, char **
 fail:
 	error = errno;
 
-	// In case of write error parent will still see that we exited
-	// unsuccessfully, but won't know why.
-	(void) safe_write_all(pipefd[1], &error, sizeof(error));
+	// In case of a write error, the parent will still see that we exited
+	// unsuccessfully, but won't know why
+	(void) xwrite(pipefd[1], &error, sizeof(error));
 
 	close(pipefd[1]);
 	_Exit(127);
@@ -221,7 +221,7 @@ pid_t bfs_spawn(const char *exe, const struct bfs_spawn *ctx, char **argv, char
 	// Parent
 	close(pipefd[1]);
 
-	ssize_t nbytes = safe_read_all(pipefd[0], &error, sizeof(error));
+	ssize_t nbytes = xread(pipefd[0], &error, sizeof(error));
 	close(pipefd[0]);
 	if (nbytes == sizeof(error)) {
 		int wstatus;
diff --git a/util.c b/util.c
index 00f5b78..19656e9 100644
--- a/util.c
+++ b/util.c
@@ -369,57 +369,48 @@ int bfs_minor(dev_t dev) {
 #endif
 }
 
-ssize_t safe_read(int fd, void *buf, size_t nbytes) {
-	for (;;) {
-		ssize_t ret = read(fd, buf, nbytes);
-		if (ret < 0 && errno == EINTR) {
-			continue;
-		}
-		return ret;
-	}
-}
-
-ssize_t safe_read_all(int fd, void *buf, size_t nbytes) {
+size_t xread(int fd, void *buf, size_t nbytes) {
 	size_t count = 0;
-	for (;;) {
+
+	while (count < nbytes) {
 		ssize_t ret = read(fd, (char *)buf + count, nbytes - count);
-		if (ret < 0 && errno == EINTR) {
-			continue;
-		}
 		if (ret < 0) {
-			return ret; // always return error < 0
-		}
-		count += ret;
-		if (ret == 0 || count == nbytes) { // EOF or success
-			return count;
+			if (errno == EINTR) {
+				continue;
+			} else {
+				break;
+			}
+		} else if (ret == 0) {
+			// EOF
+			errno = 0;
+			break;
+		} else {
+			count += ret;
 		}
 	}
-}
 
-ssize_t safe_write(int fd, const void *buf, size_t nbytes) {
-	for (;;) {
-		ssize_t ret = write(fd, buf, nbytes);
-		if (ret < 0 && errno == EINTR) {
-			continue;
-		}
-		return ret;
-	}
+	return count;
 }
 
-ssize_t safe_write_all(int fd, const void *buf, size_t nbytes)
-{
+size_t xwrite(int fd, const void *buf, size_t nbytes) {
 	size_t count = 0;
-	for (;;) {
+
+	while (count < nbytes) {
 		ssize_t ret = write(fd, (const char *)buf + count, nbytes - count);
-		if (ret < 0 && errno == EINTR) {
-			continue;
-		}
 		if (ret < 0) {
-			return ret; // always return error < 0
-		}
-		count += ret;
-		if (ret == 0 || count == nbytes) { // EOF (should never happen with write) or success
-			return count;
+			if (errno == EINTR) {
+				continue;
+			} else {
+				break;
+			}
+		} else if (ret == 0) {
+			// EOF?
+			errno = 0;
+			break;
+		} else {
+			count += ret;
 		}
 	}
+
+	return count;
 }
diff --git a/util.h b/util.h
index 7293d50..1b52513 100644
--- a/util.h
+++ b/util.h
@@ -226,23 +226,22 @@ int bfs_major(dev_t dev);
 int bfs_minor(dev_t dev);
 
 /**
- * A safe version of read() that handles interrupted system calls.
- */
-ssize_t safe_read(int fd, void *buf, size_t nbytes);
-
-/**
- * A safe version of read() that handles interrupted system calls and partial reads.
- */
-ssize_t safe_read_all(int fd, void *buf, size_t nbytes);
-
-/**
- * A safe version of write() that handles interrupted system calls.
+ * A safe version of read() that handles interrupted system calls and partial
+ * reads.
+ *
+ * @return
+ *         The number of bytes read.  A value != nbytes indicates an error
+ *         (errno != 0) or end of file (errno == 0).
  */
-ssize_t safe_write(int fd, const void *buf, size_t nbytes);
+size_t xread(int fd, void *buf, size_t nbytes);
 
 /**
- * A safe version of write() that handles interrupted system calls and partial writes.
+ * A safe version of write() that handles interrupted system calls and partial
+ * writes.
+ *
+ * @return
+           The number of bytes written.  A value != nbytes indicates an error.
  */
-ssize_t safe_write_all(int fd, const void *buf, size_t nbytes);
+size_t xwrite(int fd, const void *buf, size_t nbytes);
 
 #endif // BFS_UTIL_H
-- 
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