From 3a976c607e0bfc743a182447a688316594727197 Mon Sep 17 00:00:00 2001
From: Ian Moffett <ian@osmora.org>
Date: Wed, 27 Mar 2024 19:30:39 -0400
Subject: kernel: Implement lseek()

Signed-off-by: Ian Moffett <ian@osmora.org>
---
 sys/kern/kern_filedesc.c | 59 ++++++++++++++++++++++++++++++++++++++++++++++++
 sys/kern/kern_syscall.c  |  1 +
 2 files changed, 60 insertions(+)

(limited to 'sys/kern')

diff --git a/sys/kern/kern_filedesc.c b/sys/kern/kern_filedesc.c
index 63ffa98..6cdc1ee 100644
--- a/sys/kern/kern_filedesc.c
+++ b/sys/kern/kern_filedesc.c
@@ -338,6 +338,54 @@ read(int fd, void *buf, size_t count)
     return bytes_read;
 }
 
+/*
+ * Reposition the file offset
+ *
+ * @fd: File descriptor.
+ * @offset: Offset for the reposition
+ * @whence: SEEK_SET, SEEK_CUR, or SEEK_END
+ *
+ * TODO: Implement SEEK_END
+ */
+off_t
+lseek(int fd, off_t offset, int whence)
+{
+    struct filedesc *fd_desc;
+    struct vattr vattr;
+
+    fd_desc = fd_from_fdnum(this_td(), fd);
+
+    if (fd_desc == NULL) {
+        return -EBADF;
+    }
+
+    if (vfs_getattr(fd_desc->vnode, &vattr) != 0) {
+        return -1;
+    }
+
+    switch (whence) {
+    case SEEK_SET:
+        if (offset > vattr.size)
+            return -ESPIPE;
+
+        fd_desc->offset = offset;
+        break;
+    case SEEK_CUR:
+        if ((fd_desc->offset + offset) > vattr.size)
+            return -ESPIPE;
+
+        fd_desc->offset += offset;
+        break;
+    case SEEK_END:
+        /* TODO */
+        break;
+    default:
+        return -EINVAL;
+    }
+
+    return fd_desc->offset;
+}
+
 /*
  * arg0: int fd
  * arg1: const void *buf
@@ -418,3 +466,14 @@ sys_read(struct syscall_args *args)
     }
     return bytes_read;
 }
+
+/*
+ * arg0: fd
+ * arg1: offset:
+ * arg2: whence
+ */
+uint64_t
+sys_lseek(struct syscall_args *args)
+{
+    return lseek(args->arg0, args->arg1, args->arg2);
+}
diff --git a/sys/kern/kern_syscall.c b/sys/kern/kern_syscall.c
index 0f45469..a630195 100644
--- a/sys/kern/kern_syscall.c
+++ b/sys/kern/kern_syscall.c
@@ -46,4 +46,5 @@ uint64_t(*g_syscall_table[__MAX_SYSCALLS])(struct syscall_args *args) = {
     sys_open,
     sys_close,
     sys_read,
+    sys_lseek,
 };
-- 
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