diff --git a/lib/commonio.c b/lib/commonio.c
index 73fdb3a1..9349597a 100644
--- a/lib/commonio.c
+++ b/lib/commonio.c
@@ -140,7 +140,7 @@ static int do_lock_file (const char *file, const char *lock, bool log)
 	pid = getpid ();
 	snprintf (buf, sizeof buf, "%lu", (unsigned long) pid);
 	len = (ssize_t) strlen (buf) + 1;
-	if (write_full (fd, buf, (size_t) len) != len) {
+	if (write_full(fd, buf, len) == -1) {
 		if (log) {
 			(void) fprintf (shadow_logfd,
 			                "%s: %s file write error: %s\n",
diff --git a/lib/prototypes.h b/lib/prototypes.h
index d20abf3e..47ed2ca1 100644
--- a/lib/prototypes.h
+++ b/lib/prototypes.h
@@ -527,7 +527,7 @@ extern unsigned long active_sessions_count(const char *name,
 extern bool valid (const char *, const struct passwd *);
 
 /* write_full.c */
-extern ssize_t write_full(int fd, const void *buf, size_t count);
+extern int write_full(int fd, const void *buf, size_t count);
 
 /* xgetpwnam.c */
 extern /*@null@*/ /*@only@*/struct passwd *xgetpwnam (const char *);
diff --git a/lib/write_full.c b/lib/write_full.c
index cde52fbf..4ef902cd 100644
--- a/lib/write_full.c
+++ b/lib/write_full.c
@@ -1,7 +1,8 @@
 /*
- * SPDX-FileCopyrightText:  2023, Christian Göttsche <cgzones@googlemail.com>
+ * SPDX-FileCopyrightText: 2023, Christian Göttsche <cgzones@googlemail.com>
+ * SPDX-FileCopyrightText: 2023, Alejandro Colomar <alx@kernel.org>
  *
- * SPDX-License-Identifier:  BSD-3-Clause
+ * SPDX-License-Identifier: BSD-3-Clause
  */
 
 
@@ -9,44 +10,68 @@
 
 #ident "$Id$"
 
-#include "prototypes.h"
-
 #include <errno.h>
 #include <unistd.h>
 
+#include "prototypes.h"
+
 
 /*
- * write_full - write entire buffer
+ * SYNOPSIS
+ *	int write_full(int fd, const void *buf, size_t count);
  *
- * Write up to count bytes from the buffer starting at buf to the
- * file referred to by the file descriptor fd.
- * Retry in case of a short write.
+ * ARGUMENTS
+ *	fd	File descriptor.
+ *	buf	Source buffer to write(2) into 'fd'.
+ *	count	Size of 'buf'.
  *
- * Returns the number of bytes written on success, -1 on error.
+ * DESCRIPTION
+ *	Write 'count' bytes from the buffer starting at 'buf' to the
+ *	file referred to by 'fd'.
+ *
+ *	This function is similar to write(2), except that it retries
+ *	in case of a short write.
+ *
+ *	Since this function either performs a full write, or fails, the
+ *	return value is simpler than for write(2).
+ *
+ * RETURN VALUE
+ *	0	On success.
+ *	-1	On error.
+ *
+ * ERRORS
+ *	See write(2).
+ *
+ * CAVEATS
+ *	This function can still perform partial writes: if the function
+ *	fails in the loop after one or more write(2) calls have
+ *	succeeded, it will report a failure, but some data may have been
+ *	written.  In such a case, it's the caller's responsibility to
+ *	make sure that the partial write is not problematic, and
+ *	remediate it if it is --maybe by trying to remove the file--.
  */
-ssize_t write_full(int fd, const void *buf, size_t count) {
-	ssize_t written = 0;
+
+
+int
+write_full(int fd, const void *buf, size_t count)
+{
+	ssize_t              w;
+	const unsigned char  *p;
+
+	p = buf;
 
 	while (count > 0) {
-		ssize_t res;
-
-		res = write(fd, buf, count);
-		if (res < 0) {
-			if (errno == EINTR) {
+		w = write(fd, p, count);
+		if (w == -1) {
+			if (errno == EINTR)
 				continue;
-			}
 
-			return res;
+			return -1;
 		}
 
-		if (res == 0) {
-			break;
-		}
-
-		written += res;
-		buf = (const unsigned char*)buf + res;
-		count -= res;
+		p += w;
+		count -= w;
 	}
 
-	return written;
+	return 0;
 }
diff --git a/libmisc/copydir.c b/libmisc/copydir.c
index cc1a30d2..bbee719f 100644
--- a/libmisc/copydir.c
+++ b/libmisc/copydir.c
@@ -816,7 +816,7 @@ static int copy_file (const struct path_info *src, const struct path_info *dst,
 			break;
 		}
 
-		if (write_full (ofd, buf, cnt) < 0) {
+		if (write_full(ofd, buf, cnt) == -1) {
 			(void) close (ofd);
 			(void) close (ifd);
 			return -1;
diff --git a/libmisc/failure.c b/libmisc/failure.c
index 6fc575c1..205eec9c 100644
--- a/libmisc/failure.c
+++ b/libmisc/failure.c
@@ -86,7 +86,7 @@ void failure (uid_t uid, const char *tty, struct faillog *fl)
 	 */
 
 	if (   (lseek (fd, offset_uid, SEEK_SET) != offset_uid)
-	    || (write_full (fd, fl, sizeof *fl) != (ssize_t) sizeof *fl)
+	    || (write_full(fd, fl, sizeof *fl) == -1)
 	    || (close (fd) != 0)) {
 		SYSLOG ((LOG_WARN,
 		         "Can't write faillog entry for UID %lu in %s.",
@@ -185,7 +185,7 @@ int failcheck (uid_t uid, struct faillog *fl, bool failed)
 		fail.fail_cnt = 0;
 
 		if (   (lseek (fd, offset_uid, SEEK_SET) != offset_uid)
-		    || (write_full (fd, &fail, sizeof fail) != (ssize_t) sizeof fail)
+		    || (write_full(fd, &fail, sizeof fail) == -1)
 		    || (close (fd) != 0)) {
 			SYSLOG ((LOG_WARN,
 			         "Can't reset faillog entry for UID %lu in %s.",
diff --git a/libmisc/idmapping.c b/libmisc/idmapping.c
index ae8c4b93..b4e459e6 100644
--- a/libmisc/idmapping.c
+++ b/libmisc/idmapping.c
@@ -215,7 +215,7 @@ void write_mapping(int proc_dir_fd, int ranges, const struct map_range *mappings
 			log_get_progname(), map_file, strerror(errno));
 		exit(EXIT_FAILURE);
 	}
-	if (write_full(fd, buf, pos - buf) != (pos - buf)) {
+	if (write_full(fd, buf, pos - buf) == -1) {
 		fprintf(log_get_logfd(), _("%s: write to %s failed: %s\n"),
 			log_get_progname(), map_file, strerror(errno));
 		exit(EXIT_FAILURE);
diff --git a/libmisc/log.c b/libmisc/log.c
index cc38d6dc..fb867b27 100644
--- a/libmisc/log.c
+++ b/libmisc/log.c
@@ -82,7 +82,7 @@ void dolastlog (
 	strncpy (newlog.ll_host, host, sizeof (newlog.ll_host) - 1);
 #endif
 	if (   (lseek (fd, offset, SEEK_SET) != offset)
-	    || (write_full (fd, &newlog, sizeof newlog) != (ssize_t) sizeof newlog)
+	    || (write_full(fd, &newlog, sizeof newlog) == -1)
 	    || (close (fd) != 0)) {
 		SYSLOG ((LOG_WARN,
 		         "Can't write lastlog entry for UID %lu in %s.",
diff --git a/libmisc/utmp.c b/libmisc/utmp.c
index 7c7da697..2cccdcd2 100644
--- a/libmisc/utmp.c
+++ b/libmisc/utmp.c
@@ -97,7 +97,7 @@ static void failtmp (const char *username, const struct utmp *failent)
 	 * Append the new failure record and close the log file.
 	 */
 
-	if (   (write_full (fd, failent, sizeof *failent) != (ssize_t) sizeof *failent)
+	if (   (write_full(fd, failent, sizeof *failent) == -1)
 	    || (close (fd) != 0)) {
 		SYSLOG ((LOG_WARN,
 		         "Can't append failure of user %s to %s.",
@@ -194,7 +194,7 @@ static void updwtmp (const char *filename, const struct utmp *ut)
 
 	fd = open (filename, O_APPEND | O_WRONLY, 0);
 	if (fd >= 0) {
-		write_full (fd, ut, sizeof (*ut));
+		write_full(fd, ut, sizeof(*ut));
 		close (fd);
 	}
 }
diff --git a/src/login.c b/src/login.c
index b5562923..0f308dc1 100644
--- a/src/login.c
+++ b/src/login.c
@@ -400,7 +400,7 @@ static void exit_handler (unused int sig)
 
 static void alarm_handler (unused int sig)
 {
-	write_full (STDERR_FILENO, tmsg, strlen (tmsg));
+	write_full(STDERR_FILENO, tmsg, strlen(tmsg));
 	signal(SIGALRM, exit_handler);
 	alarm(2);
 }
diff --git a/src/su.c b/src/su.c
index 84b92468..b0334413 100644
--- a/src/su.c
+++ b/src/su.c
@@ -164,9 +164,9 @@ static void kill_child (int unused(s))
 {
 	if (0 != pid_child) {
 		(void) kill (-pid_child, SIGKILL);
-		(void) write_full (STDERR_FILENO, kill_msg, strlen (kill_msg));
+		(void) write_full(STDERR_FILENO, kill_msg, strlen(kill_msg));
 	} else {
-		(void) write_full (STDERR_FILENO, wait_msg, strlen (wait_msg));
+		(void) write_full(STDERR_FILENO, wait_msg, strlen(wait_msg));
 	}
 	_exit (255);
 }
diff --git a/src/useradd.c b/src/useradd.c
index 5b601e01..a6909927 100644
--- a/src/useradd.c
+++ b/src/useradd.c
@@ -2067,7 +2067,7 @@ static void faillog_reset (uid_t uid)
 		return;
 	}
 	if (   (lseek (fd, offset_uid, SEEK_SET) != offset_uid)
-	    || (write_full (fd, &fl, sizeof (fl)) != (ssize_t) sizeof (fl))
+	    || (write_full(fd, &fl, sizeof (fl)) == -1)
 	    || (fsync (fd) != 0)) {
 		fprintf (stderr,
 		         _("%s: failed to reset the faillog entry of UID %lu: %s\n"),
diff --git a/src/usermod.c b/src/usermod.c
index 9e896802..61cd11a8 100644
--- a/src/usermod.c
+++ b/src/usermod.c
@@ -1941,7 +1941,7 @@ static void update_lastlog (void)
 	    && (read (fd, &ll, sizeof ll) == (ssize_t) sizeof ll)) {
 		/* Copy the old entry to its new location */
 		if (   (lseek (fd, off_newuid, SEEK_SET) != off_newuid)
-		    || (write_full (fd, &ll, sizeof ll) != (ssize_t) sizeof ll)
+		    || (write_full(fd, &ll, sizeof ll) == -1)
 		    || (fsync (fd) != 0)) {
 			fprintf (stderr,
 			         _("%s: failed to copy the lastlog entry of user %lu to user %lu: %s\n"),
@@ -1957,7 +1957,7 @@ static void update_lastlog (void)
 			/* Reset the new uid's lastlog entry */
 			memzero (&ll, sizeof (ll));
 			if (   (lseek (fd, off_newuid, SEEK_SET) != off_newuid)
-			    || (write_full (fd, &ll, sizeof ll) != (ssize_t) sizeof ll)
+			    || (write_full(fd, &ll, sizeof ll) == -1)
 			    || (fsync (fd) != 0)) {
 				fprintf (stderr,
 				         _("%s: failed to copy the lastlog entry of user %lu to user %lu: %s\n"),
@@ -2001,7 +2001,7 @@ static void update_faillog (void)
 	    && (read (fd, &fl, sizeof fl) == (ssize_t) sizeof fl)) {
 		/* Copy the old entry to its new location */
 		if (   (lseek (fd, off_newuid, SEEK_SET) != off_newuid)
-		    || (write_full (fd, &fl, sizeof fl) != (ssize_t) sizeof fl)
+		    || (write_full(fd, &fl, sizeof fl) == -1)
 		    || (fsync (fd) != 0)) {
 			fprintf (stderr,
 			         _("%s: failed to copy the faillog entry of user %lu to user %lu: %s\n"),
@@ -2017,7 +2017,8 @@ static void update_faillog (void)
 			/* Reset the new uid's faillog entry */
 			memzero (&fl, sizeof (fl));
 			if (   (lseek (fd, off_newuid, SEEK_SET) != off_newuid)
-			    || (write_full (fd, &fl, sizeof fl) != (ssize_t) sizeof fl)) {
+			    || (write_full(fd, &fl, sizeof fl) == -1))
+			{
 				fprintf (stderr,
 				         _("%s: failed to copy the faillog entry of user %lu to user %lu: %s\n"),
 				         Prog, (unsigned long) user_id, (unsigned long) user_newid, strerror (errno));