4 files changed, 64 insertions, 1 deletions

diff --git a/src/user/filetest/filetest.c b/src/user/filetest/filetest.c
new file mode 100644
index 0000000..e7792ff
--- /dev/null
+++ b/src/user/filetest/filetest.c
@@ -0,0 +1,36 @@
+#include <libterm/terminal.h>
+#include <knob/file.h>
+
+#define TEST_FILE "user/test.txt"
+
+void main() {
+  struct file *f = open_file(TEST_FILE);
+  if (!f) {
+    term_add_sz("Failed to open " TEST_FILE ".\n");
+    return;
+  }
+
+  char ch;
+  if (!read_from_file(f, 1, &ch)) {
+    term_add_sz(TEST_FILE " is empty.\n");
+    close_file(f);
+    return;
+  }
+
+  term_addf(TEST_FILE " contained '%c'.\n", ch);
+
+  if (++ch >= 0x7f)
+    ch = 0x21;
+
+  seek_file_to(f, 0);
+
+  if (!write_to_file(f, 1, &ch)) {
+    term_add_sz("Failed to write to " TEST_FILE ".\n");
+    close_file(f);
+    return;
+  }
+
+  term_addf("Wrote '%c' to " TEST_FILE ".\n", ch);
+
+  close_file(f);
+}
\ No newline at end of file
diff --git a/src/user/include/knob/file.h b/src/user/include/knob/file.h
index 8862098..d283288 100644
--- a/src/user/include/knob/file.h
+++ b/src/user/include/knob/file.h
@@ -12,12 +12,14 @@ struct file *open_file(const char *path);
 void close_file(struct file *f);
 
 uint32_t read_from_file(struct file *f, uint32_t max, void *buf);
+uint32_t write_to_file(struct file *f, uint32_t max, void *buf);
 //return value and max_length don't include null terminator
 uint32_t read_line_from_file(struct file *f, char *sz, uint32_t max_length);
 uint32_t seek_file_to(struct file *f, uint32_t to);
 int32_t seek_file_by(struct file *f, int32_t by);
 
 uint32_t file_size(struct file *f) __attribute__ ((pure));
+void trunc_file(struct file *f);
 
 //return value must be manually freed, unless it is a null pointer
 _dir_info_entry_t *get_directory_info(const char *path, uint32_t *count_out);
diff --git a/src/user/include/pland/syscall.h b/src/user/include/pland/syscall.h
index 9518d09..3c4f421 100644
--- a/src/user/include/pland/syscall.h
+++ b/src/user/include/pland/syscall.h
@@ -51,7 +51,9 @@ enum _scn {
   _SCN_FIND_UNREAD_IPC,
   _SCN_WAIT_IPC_READ,
   _SCN_IS_TASK_RUNNING,
-  _SCN_GET_TIMESTAMP
+  _SCN_GET_TIMESTAMP,
+  _SCN_FILE_WRITE,
+  _SCN_SET_FILE_SIZE
 };
 
 static inline uint32_t _sc0(enum _scn eax) {
@@ -240,4 +242,12 @@ static inline uint32_t _get_timestamp() {
   return _sc0(_SCN_GET_TIMESTAMP);
 }
 
+static inline uint32_t _file_write(_file_handle_t handle, uint32_t offset, uint32_t count, const void *from) {
+  return _sc4(_SCN_FILE_WRITE, handle, offset, count, (uint32_t)from);
+}
+
+static inline void _set_file_size(_file_handle_t handle, uint32_t new_size) {
+  _sc2(_SCN_SET_FILE_SIZE, handle, new_size);
+}
+
 #endif
\ No newline at end of file
diff --git a/src/user/knob/file.c b/src/user/knob/file.c
index 3083503..283f984 100644
--- a/src/user/knob/file.c
+++ b/src/user/knob/file.c
@@ -1,4 +1,5 @@
 #include <knob/format.h>
+#include <knob/block.h>
 #include <knob/panic.h>
 #include <knob/heap.h>
 
@@ -83,6 +84,16 @@ uint32_t read_from_file(struct file *f, uint32_t max, void *buf) {
   return read;
 }
 
+uint32_t write_to_file(struct file *f, uint32_t max, void *buf) {
+  if (f->position + max > f->length)
+    _set_file_size(f->handle, f->length = f->position + max);
+
+  uint32_t written = _file_write(f->handle, f->position, max, buf);
+
+  f->position += written;
+  return written;
+}
+
 //return value and max_length don't include null terminator
 uint32_t read_line_from_file(struct file *f, char *sz, uint32_t max_length) {
   uint8_t i;
@@ -114,6 +125,10 @@ uint32_t file_size(struct file *f) {
   return f->length;
 }
 
+void trunc_file(struct file *f) {
+  _set_file_size(f->handle, f->length = f->position);
+}
+
 //return value must be manually freed, unless it is a null pointer
 _dir_info_entry_t *get_directory_info(const char *path, uint32_t *count_out) {
   uint8_t dn;