1 files changed, 67 insertions, 0 deletions
diff --git a/kernel/fs/open.c b/kernel/fs/open.c
new file mode 100644
index 0000000..fa6fe12
--- /dev/null
+++ b/kernel/fs/open.c
@@ -0,0 +1,67 @@
+#include "errno.h"
+#include "fs/fcntl.h"
+#include "fs/file.h"
+#include "fs/vfs.h"
+#include "fs/vfs_syscall.h"
+#include "fs/vnode.h"
+#include "globals.h"
+#include "util/debug.h"
+#include <fs/vnode.h>
+
+// NOTE: IF DOING MULTI-THREADED PROCS, NEED TO SYNCHRONIZE ACCESS TO FILE
+// DESCRIPTORS, AND, MORE GENERALLY SPEAKING, p_files, IN PARTICULAR IN THIS
+// FUNCTION AND ITS CALLERS.
+/*
+ * Go through curproc->p_files and find the first null entry.
+ * If one exists, set fd to that index and return 0.
+ *
+ * Error cases get_empty_fd is responsible for generating:
+ *  - EMFILE: no empty file descriptor
+ */
+long get_empty_fd(int *fd)
+{
+    for (*fd = 0; *fd < NFILES; (*fd)++)
+    {
+        if (!curproc->p_files[*fd])
+        {
+            return 0;
+        }
+    }
+    *fd = -1;
+    return -EMFILE;
+}
+
+/*
+ * Open the file at the provided path with the specified flags.
+ *
+ * Returns the file descriptor on success, or error cases:
+ *  - EINVAL: Invalid oflags
+ *  - EISDIR: Trying to open a directory with write access
+ *  - ENXIO: Blockdev or chardev vnode does not have an actual underlying device
+ *  - ENOMEM: Not enough kernel memory (if fcreate() fails)
+ *
+ * Hints:
+ * 1) Use get_empty_fd() to get an available fd.
+ * 2) Use namev_open() with oflags, mode S_IFREG, and devid 0.
+ * 3) Check for EISDIR and ENXIO errors.
+ * 4) Convert oflags (O_RDONLY, O_WRONLY, O_RDWR, O_APPEND) into corresponding
+ *    file access flags (FMODE_READ, FMODE_WRITE, FMODE_APPEND). 
+ * 5) Use fcreate() to create and initialize the corresponding file descriptor
+ *    with the vnode from 2) and the mode from 4).
+ *
+ * When checking oflags, you only need to check that the read and write
+ * permissions are consistent. However, because O_RDONLY is 0 and O_RDWR is 2,
+ * there's no way to tell if both were specified. So, you really only need
+ * to check if O_WRONLY and O_RDWR were specified. 
+ * 
+ * If O_TRUNC specified and the vnode represents a regular file, make sure to call the
+ * the vnode's truncate routine (to reduce the size of the file to 0).
+ *
+ * If a vnode represents a chardev or blockdev, then the appropriate field of
+ * the vnode->vn_dev union will point to the device. Otherwise, the union will be NULL.
+ */
+long do_open(const char *filename, int oflags)
+{
+    NOT_YET_IMPLEMENTED("VFS: ***none***");
+    return -1;
+}