libc: unistd: Add lseek system call interface

Signed-off-by: Ian Moffett <ian@osmora.org>

2 files changed, 57 insertions, 0 deletions

diff --git a/src/lib/libc/include/unistd.h b/src/lib/libc/include/unistd.h
index b668d5b..61b437c 100644
--- a/src/lib/libc/include/unistd.h
+++ b/src/lib/libc/include/unistd.h
@@ -30,6 +30,7 @@
 #ifndef _UNISTD_H
 #define _UNISTD_H 1
 
+#include <sys/seek.h>
 #include <stddef.h>
 
 /* Standard stream file numbers */
@@ -74,4 +75,13 @@ ssize_t write(int fd, const void *buf, size_t count);
  */
 ssize_t read(int fd, void *buf, size_t count);
 
+/*
+ * Reposition the file offset of a file
+ *
+ * @fd: File descriptor to reposition
+ * @offset: Offset to move `fd' to
+ * @whence: How it should be repositioned
+ */
+off_t lseek(int fd, off_t offset, int whence);
+
 #endif  /* _UNISTD_H */
diff --git a/src/lib/libc/src/unistd/lseek.c b/src/lib/libc/src/unistd/lseek.c
new file mode 100644
index 0000000..ade0a1e
--- /dev/null
+++ b/src/lib/libc/src/unistd/lseek.c
@@ -0,0 +1,47 @@
+/*
+ * Copyright (c) 2025 Ian Marco Moffett and L5 engineers
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice,
+ *    this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of the project nor the names of its
+ *    contributors may be used to endorse or promote products derived from
+ *    this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <sys/syscall.h>
+#include <unistd.h>
+#include <errno.h>
+
+off_t
+lseek(int fd, off_t offset, int whence)
+{
+    if (fd < 0) {
+        return -EBADF;
+    }
+
+    return syscall(
+        SYS_lseek,
+        fd,
+        offset,
+        whence
+    );
+}