zed: replace zed_file_write_n() with write(2), purge it

We set SA_RESTART early on, which will prevent EINTRs (indeed, to the
point of needing to clear it in the reaper, since it interferes with
pause(2)), which is the only error zed_file_write_n() actually handled
(plus, the pid write is no bigger than 12 bytes anyway)

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Closes #11834

cmd/zed/zed_conf.c

@@ -515,7 +515,7 @@ zed_conf_write_pid(struct zed_conf *zcp)
 		errno = ERANGE;
 		zed_log_msg(LOG_ERR, "Failed to write PID file \"%s\": %s",
 		    zcp->pid_file, strerror(errno));
-	} else if (zed_file_write_n(zcp->pid_fd, buf, n) != n) {
+	} else if (write(zcp->pid_fd, buf, n) != n) {
 		zed_log_msg(LOG_ERR, "Failed to write PID file \"%s\": %s",
 		    zcp->pid_file, strerror(errno));
 	} else if (fdatasync(zcp->pid_fd) < 0) {

cmd/zed/zed_file.c

@@ -24,33 +24,6 @@
 #include "zed_file.h"
 #include "zed_log.h"
 
-/*
- * Write [n] bytes from [buf] out to [fd].
- * Return the number of bytes written, or -1 on error.
- */
-ssize_t
-zed_file_write_n(int fd, void *buf, size_t n)
-{
-	const unsigned char *p;
-	size_t n_left;
-	ssize_t n_written;
-
-	p = buf;
-	n_left = n;
-	while (n_left > 0) {
-		if ((n_written = write(fd, p, n_left)) < 0) {
-			if (errno == EINTR)
-				continue;
-			else
-				return (-1);
-
-		}
-		n_left -= n_written;
-		p += n_written;
-	}
-	return (n);
-}
-
 /*
  * Set an exclusive advisory lock on the open file descriptor [fd].
  * Return 0 on success, 1 if a conflicting lock is held by another process,

cmd/zed/zed_file.h

@@ -18,8 +18,6 @@
 #include <sys/types.h>
 #include <unistd.h>
 
-ssize_t zed_file_write_n(int fd, void *buf, size_t n);
-
 int zed_file_lock(int fd);
 
 int zed_file_unlock(int fd);