From 599ef07b89aa31c089398922ef65804f47f44b55 Mon Sep 17 00:00:00 2001
From: Ian Moffett <ian@osmora.org>
Date: Mon, 22 Jul 2024 14:31:35 -0400
Subject: kernel: vfs_syscalls: Add sys_read()

Signed-off-by: Ian Moffett <ian@osmora.org>
---
 sys/include/sys/syscall.h |  1 +
 sys/include/sys/vfs.h     |  1 +
 sys/kern/kern_syscall.c   |  1 +
 sys/kern/vfs_syscalls.c   | 83 +++++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 86 insertions(+)

(limited to 'sys')

diff --git a/sys/include/sys/syscall.h b/sys/include/sys/syscall.h
index e4a72f2..9aa96e7 100644
--- a/sys/include/sys/syscall.h
+++ b/sys/include/sys/syscall.h
@@ -38,6 +38,7 @@
 #define SYS_none    0
 #define SYS_exit    1
 #define SYS_open    2
+#define SYS_read    3
 
 #if defined(_KERNEL)
 /* Syscall return value and arg type */
diff --git a/sys/include/sys/vfs.h b/sys/include/sys/vfs.h
index 16c7795..52d35f3 100644
--- a/sys/include/sys/vfs.h
+++ b/sys/include/sys/vfs.h
@@ -36,6 +36,7 @@
 #if defined(_KERNEL)
 
 scret_t sys_open(struct syscall_args *scargs);
+scret_t sys_read(struct syscall_args *scargs);
 
 #endif  /* _KERNEL */
 #endif  /* !_SYS_VFS_H_ */
diff --git a/sys/kern/kern_syscall.c b/sys/kern/kern_syscall.c
index 2c81d2c..416a8ec 100644
--- a/sys/kern/kern_syscall.c
+++ b/sys/kern/kern_syscall.c
@@ -36,6 +36,7 @@ scret_t(*g_sctab[])(struct syscall_args *) = {
     NULL,       /* SYS_none */
     sys_exit,   /* SYS_exit */
     sys_open,   /* SYS_open */
+    sys_read,   /* SYS_read */
 };
 
 const size_t MAX_SYSCALLS = NELEM(g_sctab);
diff --git a/sys/kern/vfs_syscalls.c b/sys/kern/vfs_syscalls.c
index c2ae580..371c1a5 100644
--- a/sys/kern/vfs_syscalls.c
+++ b/sys/kern/vfs_syscalls.c
@@ -32,6 +32,7 @@
 #include <sys/types.h>
 #include <sys/systm.h>
 #include <sys/errno.h>
+#include <sys/sio.h>
 #include <sys/filedesc.h>
 #include <sys/namei.h>
 #include <sys/proc.h>
@@ -41,6 +42,24 @@
 #include <assert.h>
 #include <string.h>
 
+/*
+ * Fetch a file descriptor from a file descriptor
+ * number.
+ *
+ * @fdno: File descriptor to fetch
+ */
+static struct filedesc *
+fd_get(int fdno)
+{
+    struct proc *td = this_td();
+
+    if (fdno < 0 || fdno > PROC_MAX_FILEDES) {
+        return NULL;
+    }
+
+    return td->fds[fdno];
+}
+
 /*
  * Allocate a file descriptor.
  *
@@ -118,3 +137,67 @@ sys_open(struct syscall_args *scargs)
     filedes->vp = nd.vp;
     return filedes->fdno;
 }
+
+/*
+ * arg0: fd
+ * arg1: buf
+ * arg2: count
+ */
+scret_t
+sys_read(struct syscall_args *scargs)
+{
+    int fd;
+    char *buf, *kbuf = NULL;
+    size_t count;
+    struct filedesc *filedes;
+    struct sio_txn sio;
+    scret_t retval = 0;
+
+    fd = scargs->arg0;
+    buf = (char *)scargs->arg1;
+    count = scargs->arg2;
+
+    if (count > SSIZE_MAX) {
+        retval = -EINVAL;
+        goto done;
+    }
+
+    filedes = fd_get(fd);
+    kbuf = dynalloc(count);
+
+    if (kbuf == NULL) {
+        retval = -ENOMEM;
+        goto done;
+    }
+
+    if (filedes == NULL) {
+        retval = -EBADF;
+        goto done;
+    }
+
+    if (filedes->is_dir) {
+        retval = -EISDIR;
+        goto done;
+    }
+
+    sio.len = count;
+    sio.buf = kbuf;
+    sio.offset = filedes->offset;
+
+    if ((count = vfs_vop_read(filedes->vp, &sio)) < 0) {
+        retval = -EIO;
+        goto done;
+    }
+
+    if (copyout(kbuf, buf, count) < 0) {
+        retval = -EFAULT;
+        goto done;
+    }
+
+    retval = count;
+done:
+    if (kbuf != NULL) {
+        dynfree(kbuf);
+    }
+    return retval;
+}
-- 
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