From e9edee7206645adcd48b91aae6ef4734f2e98254 Mon Sep 17 00:00:00 2001
From: Ian Moffett <ian@osmora.org>
Date: Tue, 26 Mar 2024 18:18:33 -0400
Subject: kernel: Add initial open() implementation

Signed-off-by: Ian Moffett <ian@osmora.org>
---
 sys/include/sys/filedesc.h |  7 ++++++
 sys/include/sys/syscall.h  |  1 +
 sys/kern/kern_filedesc.c   | 62 ++++++++++++++++++++++++++++++++++++++++++++++
 sys/kern/kern_syscall.c    |  1 +
 4 files changed, 71 insertions(+)

(limited to 'sys')

diff --git a/sys/include/sys/filedesc.h b/sys/include/sys/filedesc.h
index 49d8d52..6eb500e 100644
--- a/sys/include/sys/filedesc.h
+++ b/sys/include/sys/filedesc.h
@@ -35,6 +35,10 @@
 #include <sys/syscall.h>
 #include <sys/types.h>
 
+#define O_RDONLY 0x00000
+#define O_WRONLY 0x00001
+#define O_RDWR   0x00002
+
 struct proc;
 
 struct filedesc {
@@ -50,7 +54,10 @@ int fd_alloc(struct proc *td, struct filedesc **fd_out);
 struct filedesc *fd_from_fdnum(const struct proc *td, int fdno);
 void fd_close_fdnum(struct proc *td, int fdno);
 ssize_t write(int fd, const void *buf, size_t count);
+int open(const char *pathname, int oflag);
+
 uint64_t sys_write(struct syscall_args *args);
+uint64_t sys_open(struct syscall_args *args);
 #endif
 
 #endif
diff --git a/sys/include/sys/syscall.h b/sys/include/sys/syscall.h
index e75b193..0f066e5 100644
--- a/sys/include/sys/syscall.h
+++ b/sys/include/sys/syscall.h
@@ -39,6 +39,7 @@
 enum {
     SYS_exit = 1,
     SYS_write,
+    SYS_open,
     __MAX_SYSCALLS
 };
 
diff --git a/sys/kern/kern_filedesc.c b/sys/kern/kern_filedesc.c
index 72d294d..c429125 100644
--- a/sys/kern/kern_filedesc.c
+++ b/sys/kern/kern_filedesc.c
@@ -33,6 +33,7 @@
 #include <sys/errno.h>
 #include <sys/system.h>
 #include <sys/syslog.h>
+#include <sys/vfs.h>
 #include <sys/vnode.h>
 #include <vm/dynalloc.h>
 #include <dev/vcons/vcons.h>
@@ -258,6 +259,44 @@ cleanup:
     return ret;
 }
 
+/*
+ * Open a file and return a file descriptor.
+ *
+ * @pathname: File path.
+ * @oflag: Flags.
+ */
+int
+open(const char *pathname, int oflag)
+{
+    struct vnode *vp;
+    struct filedesc *fd;
+    int status;
+
+    /*
+     * Attempt to create a vnode and allocate a
+     * file descriptor
+     */
+    if ((status = vfs_path_to_node(pathname, &vp)) != 0) {
+        return status;
+    }
+    if ((status = fd_alloc(this_td(), &fd)) != 0) {
+        return status;
+    }
+
+    /*
+     * TODO: Handle more flags... For now we only support
+     *       O_RDONLY, so deny other flags.
+     */
+    if ((oflag & ~O_RDONLY) != 0){
+        fd_close_fdnum(this_td(), fd->fdno);
+        return -EACCES;
+    }
+
+    fd->vnode = vp;
+    fd->is_dir = (vp->type == VDIR);
+    return fd->fdno;
+}
+
 /*
  * arg0: int fd
  * arg1: const void *buf
@@ -268,3 +307,26 @@ sys_write(struct syscall_args *args)
 {
     return write(args->arg0, (void *)args->arg1, args->arg2);
 }
+
+/*
+ * arg0: const char *pathname
+ * arg1: int oflag
+ */
+uint64_t
+sys_open(struct syscall_args *args)
+{
+    char *pathbuf = dynalloc(sizeof(char) * PATH_MAX);
+    int ret;
+
+    if (pathbuf == NULL) {
+        return -ENOMEM;
+    }
+
+    if (copyinstr(args->arg0, pathbuf, PATH_MAX) != 0) {
+        invalid_uaddr(args->arg0);
+    }
+
+    ret = open(pathbuf, args->arg1);
+    dynfree(pathbuf);
+    return ret;
+}
diff --git a/sys/kern/kern_syscall.c b/sys/kern/kern_syscall.c
index 2659448..dc37274 100644
--- a/sys/kern/kern_syscall.c
+++ b/sys/kern/kern_syscall.c
@@ -43,4 +43,5 @@ sys_exit(struct syscall_args *args)
 uint64_t(*g_syscall_table[__MAX_SYSCALLS])(struct syscall_args *args) = {
     sys_exit,
     sys_write,
+    sys_open,
 };
-- 
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