[file_handler] Bug fixes: GDT overflow, invalid last block. Add ferror

Author: scopeInfinity

src/fs/ffs.c

@@ -94,9 +94,10 @@ int fetch_file_content(
 
     // fetch file entry
     int file_size = entry->content.filesize;
-    int block_count = file_size/FS_BLOCK_SIZE;
+    int block_count = (file_size+FS_BLOCK_SIZE-1)/FS_BLOCK_SIZE;
     if(file_block_id >= block_count) {
-        return -1;
+        // zero block read
+        return 0;
     }
 
     int err = partition_read_block(

src/kernel/syscall/file_handler.c

@@ -60,7 +60,7 @@ int _file_handler_read(int user_ds, int file_id, char _us_buffer[FILEIO_BUFFER_S
         return 0;
     }
     len = min(len, FILEIO_BUFFER_SIZE); // guard for _us_buffer
-
+    len = min(len, FS_BLOCK_SIZE-byte_index_block); // skip already read content of the block
     syscall_strncpy_kernel_to_user(user_ds, _us_buffer, block+byte_index_block, len);
     return len;
 }

src/usr/include/stdio.h

@@ -22,6 +22,9 @@ typedef struct FILE {
 
     // 0 => start of file
     int cursor;
+
+    // store last error code
+    int err;
 } FILE;
 
 // TODO: Add API for reading list of files.
@@ -41,4 +44,7 @@ typedef struct FILE {
 FILE *fopen(char *filename, char *mode);
 int fgetc(FILE *file);
 char *fgets(char *buf, size_t n, FILE *file);
-int fclose(FILE *file);
+int fclose(FILE *file);
+
+int ferror(FILE *file);
+void clearerror(FILE *file);

src/usr/lib/stdio.c

@@ -131,6 +131,7 @@ FILE *fopen(char *filename, char *mode) {
     handler->file_handler_id = fh_id;
     handler->file_id = file_id;
     handler->cursor = 0;
+    handler->err = 0;
     return handler;
 }
 
@@ -152,10 +153,15 @@ char *fgets(char *buf, size_t n, FILE *file) {
         int count = SYSCALL_A4(SYSCALL_FILE_OP, SYSCALL_FILE_SUB_READBUFFER, file->file_id, _buffer, file->cursor);
         if (count < 0) {
             // error
+            file->err = count;
             return NULL;
         }
         if (count == 0) {
             // EOF
+            if(og_buf==buf) {
+                // no new characters read
+                return NULL;
+            }
             break;
         }
 
@@ -164,11 +170,11 @@ char *fgets(char *buf, size_t n, FILE *file) {
         int found_newline = 0;
         for (size_t i = 0; i < max_iterations; i++) {
             char_read_count++;
+            *(buf++)=_buffer[i];
             if(_buffer[i]=='\n') {
                 found_newline = 1;
                 break;
             }
-            *(buf++)=_buffer[i];
         }
         file->cursor += char_read_count;
         n-=char_read_count;
@@ -181,3 +187,11 @@ char *fgets(char *buf, size_t n, FILE *file) {
 int fgetc(FILE *file) {
 
 }
+
+int ferror(FILE *file) {
+    return file->err;
+}
+
+void clearerror(FILE *file) {
+    file->err=0;
+}

src/usr/local/src/cat.c

@@ -11,10 +11,14 @@ void process(char filename[]) {
     char buffer[80];
     while(1) {
         if (!fgets(buffer, sizeof(buffer), handler)) {
+            int err = ferror(handler);
+            if(err) {
+                printf("Error: failed to read next chunk, code %d\n", err);
+                exit(err);
+            }
             break;
         }
         puts(buffer);
-        putchar('\n');
     }
     fclose(handler);
 }

tests/app/cat_test.sh

@@ -7,4 +7,4 @@ QEMU_SCREENSHOT_NAME="cat_test.ppm"
 python3 -m tests.qemu.monitor -p ${MONITOR_PORT:?} -sc cat readme.md
 
 test_create_screen_dump
-test_screen_content $LINENO "Use make to build binaries and image files"
+test_screen_content $LINENO "Execute QEMU in debug mode and setup GDB server"