From 6371724809b057b25a4efd6c022e7d95068c42f1 Mon Sep 17 00:00:00 2001
From: dzwdz
Date: Mon, 20 Sep 2021 19:30:37 +0200
Subject: add an offset parameter to read() and write()

---
 src/init/main.c     |  8 ++++----
 src/init/syscalls.c |  8 ++++----
 src/init/tar.c      | 14 ++++++++++----
 3 files changed, 18 insertions(+), 12 deletions(-)

(limited to 'src/init')

diff --git a/src/init/main.c b/src/init/main.c
index 66d4b2b..1e2d16f 100644
--- a/src/init/main.c
+++ b/src/init/main.c
@@ -4,7 +4,7 @@
 #include <stdint.h>
 
 #define argify(str) str, sizeof(str) - 1
-#define log(str) _syscall_write(tty_fd, argify(str))
+#define log(str) _syscall_write(tty_fd, argify(str), 0)
 
 extern char _bss_start; // provided by the linker
 extern char _bss_end;
@@ -34,15 +34,15 @@ void read_file(const char *path, size_t len) {
 	static char buf[64];
 	int buf_len = 64;
 
-	_syscall_write(tty_fd, path, len);
+	_syscall_write(tty_fd, path, len, 0);
 	log(": ");
 	if (fd < 0) {
 		log("couldn't open.\n");
 		return;
 	}
 
-	buf_len = _syscall_read(fd, buf, buf_len);
-	_syscall_write(tty_fd, buf, buf_len);
+	buf_len = _syscall_read(fd, buf, buf_len, 0);
+	_syscall_write(tty_fd, buf, buf_len, 0);
 
 	_syscall_close(fd);
 }
diff --git a/src/init/syscalls.c b/src/init/syscalls.c
index 7d0fef9..f32594e 100644
--- a/src/init/syscalls.c
+++ b/src/init/syscalls.c
@@ -22,12 +22,12 @@ int _syscall_mount(handle_t handle, const char __user *path, int len) {
 	return _syscall(_SYSCALL_MOUNT, handle, (int)path, len, 0);
 }
 
-int _syscall_read(handle_t handle, char __user *buf, int len) {
-	return _syscall(_SYSCALL_READ, handle, (int)buf, len, 0);
+int _syscall_read(handle_t handle, char __user *buf, int len, int offset) {
+	return _syscall(_SYSCALL_READ, handle, (int)buf, len, offset);
 }
 
-int _syscall_write(handle_t handle, const char __user *buf, int len) {
-	return _syscall(_SYSCALL_WRITE, handle, (int)buf, len, 0);
+int _syscall_write(handle_t handle, const char __user *buf, int len, int offset) {
+	return _syscall(_SYSCALL_WRITE, handle, (int)buf, len, offset);
 }
 
 int _syscall_close(handle_t handle) {
diff --git a/src/init/tar.c b/src/init/tar.c
index 74e4c83..691768c 100644
--- a/src/init/tar.c
+++ b/src/init/tar.c
@@ -24,7 +24,13 @@ void tar_driver(handle_t back, void *base) {
 
 			case VFSOP_READ: {
 				void *meta = (void*)res.id;
-				_syscall_fs_respond(meta + 512, tar_size(meta));
+				int size = tar_size(meta);
+				if (res.offset < 0 || res.offset > size) {
+					// TODO support negative offsets
+					_syscall_fs_respond(NULL, -1);
+				} else {
+					_syscall_fs_respond(meta + 512 + res.offset, size - res.offset);
+				}
 				break;
 			}
 
@@ -38,14 +44,14 @@ void tar_driver(handle_t back, void *base) {
 	while (0 == memcmp(base + 257, "ustar", 5)) {
 		int size = oct_parse(base + 124, 12);
 
-		_syscall_write(tty_fd, base, 100);
-		_syscall_write(tty_fd, " ", 1);
+		_syscall_write(tty_fd, base, 100, 0);
+		_syscall_write(tty_fd, " ", 1, 0);
 
 		base += 512;                 // skip metadata sector
 		base += (size + 511) & ~511; // skip file (size rounded up to 512)
 		// TODO might pagefault if the last sector was at a page boundary
 	}
-	_syscall_write(tty_fd, "done.", 5);
+	_syscall_write(tty_fd, "done.", 5, 0);
 }
 
 static int tar_open(const char *path, int len, void *base, size_t base_len) {
-- 
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