From d68537c1ca22d58f1c219d970d5aa462df9e0c6b Mon Sep 17 00:00:00 2001
From: Ian Moffett <ian@osmora.org>
Date: Sat, 22 Feb 2025 02:18:33 -0500
Subject: kernel: vfs: Add support for write()

Signed-off-by: Ian Moffett <ian@osmora.org>
---
 sys/kern/kern_descrip.c | 50 ++++++++++++++++++++++++++++++++++++++++++-------
 sys/kern/kern_syscall.c |  1 +
 sys/kern/vfs_subr.c     | 13 +++++++++++++
 sys/kern/vfs_syscalls.c | 12 ++++++++++++
 4 files changed, 69 insertions(+), 7 deletions(-)

(limited to 'sys/kern')

diff --git a/sys/kern/kern_descrip.c b/sys/kern/kern_descrip.c
index d1ed044..201db3e 100644
--- a/sys/kern/kern_descrip.c
+++ b/sys/kern/kern_descrip.c
@@ -31,6 +31,7 @@
 #include <sys/errno.h>
 #include <sys/proc.h>
 #include <sys/limits.h>
+#include <sys/fcntl.h>
 #include <sys/namei.h>
 #include <sys/filedesc.h>
 #include <sys/systm.h>
@@ -135,15 +136,16 @@ fd_close(unsigned int fd)
 }
 
 /*
- * Read bytes from a file using a file
+ * Read/write bytes to/from a file using a file
  * descriptor number.
  *
  * @fd: File descriptor number.
- * @buf: Buffer to read into.
+ * @buf: Buffer with data to read/write
  * @count: Number of bytes to read.
+ * @write: Set to 1 for writes
  */
-int
-fd_read(unsigned int fd, void *buf, size_t count)
+static int
+fd_rw(unsigned int fd, void *buf, size_t count, uint8_t write)
 {
     char *kbuf = NULL;
     struct filedesc *filedes;
@@ -173,13 +175,34 @@ fd_read(unsigned int fd, void *buf, size_t count)
         goto done;
     }
 
+    /* Check if this violates the file seal */
+    if (!ISSET(filedes->flags, O_ALLOW_WR) && write) {
+        return -EPERM;
+    } else if (ISSET(O_RDONLY, filedes->flags) && write) {
+        return -EPERM;
+    }
+
     sio.len = count;
     sio.buf = kbuf;
     sio.offset = filedes->offset;
 
-    if ((count = vfs_vop_read(filedes->vp, &sio)) < 0) {
-        retval = -EIO;
-        goto done;
+    if (write) {
+        /* Copy in user buffer */
+        if (copyin(buf, kbuf, count) < 0) {
+            retval = -EFAULT;
+            goto done;
+        }
+
+        /* Call VFS write hook */
+        if ((count = vfs_vop_write(filedes->vp, &sio)) < 0) {
+            retval = -EIO;
+            goto done;
+        }
+    } else {
+        if ((count = vfs_vop_read(filedes->vp, &sio)) < 0) {
+            retval = -EIO;
+            goto done;
+        }
     }
 
     if (copyout(kbuf, buf, count) < 0) {
@@ -195,6 +218,18 @@ done:
     return retval;
 }
 
+int
+fd_read(unsigned int fd, void *buf, size_t count)
+{
+    return fd_rw(fd, buf, count, 0);
+}
+
+int
+fd_write(unsigned int fd, void *buf, size_t count)
+{
+    return fd_rw(fd, buf, count, 1);
+}
+
 /*
  * Open a file and get a file descriptor
  * number.
@@ -224,6 +259,7 @@ fd_open(const char *pathname, int flags)
     }
 
     filedes->vp = nd.vp;
+    filedes->flags = flags;
     return filedes->fdno;
 }
 
diff --git a/sys/kern/kern_syscall.c b/sys/kern/kern_syscall.c
index 1d961a7..986d82a 100644
--- a/sys/kern/kern_syscall.c
+++ b/sys/kern/kern_syscall.c
@@ -41,6 +41,7 @@ scret_t(*g_sctab[])(struct syscall_args *) = {
     sys_close,  /* SYS_close */
     sys_stat,   /* SYS_stat */
     sys_sysctl, /* SYS_sysctl */
+    sys_write,  /* SYS_write */
 };
 
 const size_t MAX_SYSCALLS = NELEM(g_sctab);
diff --git a/sys/kern/vfs_subr.c b/sys/kern/vfs_subr.c
index f67bcfe..da0a4f9 100644
--- a/sys/kern/vfs_subr.c
+++ b/sys/kern/vfs_subr.c
@@ -166,6 +166,19 @@ vfs_vop_read(struct vnode *vp, struct sio_txn *sio)
     return vops->read(vp, sio);
 }
 
+int
+vfs_vop_write(struct vnode *vp, struct sio_txn *sio)
+{
+    const struct vops *vops = vp->vops;
+
+    if (vops == NULL)
+        return -EIO;
+    if (vops->write == NULL)
+        return -EIO;
+
+    return vops->write(vp, sio);
+}
+
 int
 vfs_vop_getattr(struct vnode *vp, struct vop_getattr_args *args)
 {
diff --git a/sys/kern/vfs_syscalls.c b/sys/kern/vfs_syscalls.c
index fa613c2..6f2d683 100644
--- a/sys/kern/vfs_syscalls.c
+++ b/sys/kern/vfs_syscalls.c
@@ -128,6 +128,18 @@ sys_read(struct syscall_args *scargs)
         scargs->arg2);
 }
 
+/*
+ * arg0: fd
+ * arg1: buf
+ * arg2: count
+ */
+scret_t
+sys_write(struct syscall_args *scargs)
+{
+    return fd_write(scargs->arg0, (void *)scargs->arg1,
+        scargs->arg2);
+}
+
 /*
  * arg0: path
  * arg1: buf
-- 
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