lib: fs: implement fs.seek()

lib/libfs/context.c

@@ -90,6 +90,7 @@ struct fs_context *fs_context_create(struct fs_allocator *alloc)
 	ctx->ctx_vtable.close = fs_msg_close;
 	ctx->ctx_vtable.read = fs_msg_read;
 	ctx->ctx_vtable.write = fs_msg_write;
+	ctx->ctx_vtable.seek = fs_msg_seek;
 	ctx->ctx_vtable.map = fs_msg_map;
 
 	return ctx;

lib/libfs/interface.h

@@ -38,6 +38,14 @@ extern kern_status_t fs_msg_write(
 	size_t *out_nr_written,
 	void *arg);
 
+extern kern_status_t fs_msg_seek(
+	xpc_context_t *ctx,
+	const xpc_endpoint_t *sender,
+	off_t offset,
+	int origin,
+	int *out_err,
+	off_t *out_new_pos,
+	void *arg);
 extern kern_status_t fs_msg_map(
 	xpc_context_t *ctx,
 	const xpc_endpoint_t *sender,

lib/libfs/interface/seek.c

@@ -0,0 +1,52 @@
+#include "../file.h"
+
+#include <errno.h>
+#include <fs/context.h>
+#include <fs/file.h>
+#include <fs/status.h>
+#include <sys/types.h>
+
+extern kern_status_t fs_msg_seek(
+	xpc_context_t *xpc,
+	const xpc_endpoint_t *sender,
+	off_t rel_offset,
+	int origin,
+	int *out_err,
+	off_t *out_new_pos,
+	void *arg)
+{
+	struct fs_context *ctx = arg;
+	struct fs_file *f = fs_context_get_file(ctx, sender->e_port);
+	if (!f) {
+		*out_err = EBADF;
+		return KERN_OK;
+	}
+
+	off_t new_offset = 0;
+
+	switch (origin) {
+	case SEEK_SET:
+		new_offset = rel_offset;
+		break;
+	case SEEK_CUR:
+		new_offset = f->f_seek + rel_offset;
+		break;
+	case SEEK_END:
+		new_offset = f->f_inode->i_size + rel_offset;
+		break;
+	default:
+		*out_err = EINVAL;
+		return KERN_OK;
+	}
+
+	if (new_offset > f->f_inode->i_size) {
+		*out_err = EINVAL;
+		return KERN_OK;
+	}
+
+	f->f_seek = new_offset;
+	*out_err = SUCCESS;
+	*out_new_pos = new_offset;
+
+	return KERN_OK;
+}