lib - a pwrite() implementation (Contributed by Buccapatnam Tirumala, Gautam)

bengras · bengras · commit 24a5f48921a0 · 2010-06-22T22:04:43.000Z
diff --git a/include/unistd.h b/include/unistd.h
@@ -147,6 +147,7 @@ _PROTOTYPE( int tcsetpgrp, (int _fd, pid_t _pgrp_id)			);
 _PROTOTYPE( char *ttyname, (int _fd)					);
 _PROTOTYPE( int unlink, (const char *_path)				);
 _PROTOTYPE( ssize_t write, (int _fd, const void *_buf, size_t _n)	);
+_PROTOTYPE( ssize_t pwrite, (int _fd, const void *_buf, size_t _n, off_t _offset));
 _PROTOTYPE( int truncate, (const char *_path, off_t _length)		);
 _PROTOTYPE( int ftruncate, (int _fd, off_t _length)			);
 _PROTOTYPE( int nice, (int _incr)					);
diff --git a/lib/libc/posix/Makefile.inc b/lib/libc/posix/Makefile.inc
@@ -107,4 +107,5 @@ SRCS+= 	 \
 	nice.c \
 	priority.c \
 	pread.c \
+	pwrite.c \
 	usleep.c
diff --git a/lib/libc/posix/pwrite.c b/lib/libc/posix/pwrite.c
@@ -0,0 +1,26 @@
+#include <lib.h>
+#include <unistd.h>
+
+ssize_t pwrite(int fd, const void *buffer, size_t nbytes, off_t where)
+{
+	off_t here;
+	ssize_t w;
+
+	if((here = lseek(fd, 0, SEEK_CUR)) < 0)
+		return -1;
+
+	if(lseek(fd, where, SEEK_SET) < 0)
+		return -1;
+
+	if((w=write(fd, buffer, nbytes)) < 0) {
+		int e = errno;
+		lseek(fd, here, SEEK_SET);
+		errno = e;
+		return -1;
+	}
+
+	if(lseek(fd, here, SEEK_SET) < 0)
+		return -1;
+
+	return w;
+}
