From ed5e50f7402842716d00f45faff15be4d8e5bfb6 Mon Sep 17 00:00:00 2001
From: Ian Moffett <ian@osmora.org>
Date: Thu, 11 Jul 2024 21:31:36 -0400
Subject: kernel: namei: Allow lookups farther than '/'

Signed-off-by: Ian Moffett <ian@osmora.org>
---
 sys/kern/vfs_lookup.c | 159 +++++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 151 insertions(+), 8 deletions(-)

diff --git a/sys/kern/vfs_lookup.c b/sys/kern/vfs_lookup.c
index 83924c6..658e908 100644
--- a/sys/kern/vfs_lookup.c
+++ b/sys/kern/vfs_lookup.c
@@ -29,25 +29,141 @@
 
 #include <sys/namei.h>
 #include <sys/vnode.h>
+#include <sys/mount.h>
 #include <sys/errno.h>
 #include <vm/dynalloc.h>
 #include <string.h>
 
+/*
+ * Fetches the filename within a path at
+ * the nth index denoted by `idx'
+ *
+ * Returns memory allocated by dynalloc()
+ * containing the filename.
+ *
+ * XXX: MUST FREE RETURN VALUE WITH dynfree() WHEN
+ *      DONE!
+ */
+static char *
+vfs_get_fname_at(const char *path, size_t idx)
+{
+    size_t pathlen = strlen(path);
+    size_t fname_len;
+
+    char *path_tmp = dynalloc(pathlen + 2);
+    char *ret = NULL;
+    char *start_ptr, *ptr;
+
+    /* Make one-based */
+    ++idx;
+
+    if (path_tmp == NULL) {
+        return NULL;
+    }
+
+    ptr = path_tmp;
+    memcpy(path_tmp, path, pathlen + 1);
+
+    /*
+     * We want to by default have a '/' at the end
+     * to keep the parsing logic from getting more
+     * complicated than it needs to be.
+     */
+    path_tmp[pathlen] = '/';
+    path_tmp[pathlen + 1] = '\0';
+
+    /* Skip any leading slashes */
+    while (*ptr == '/')
+        ++ptr;
+
+    start_ptr = ptr;
+
+    /* Get each filename */
+    while (*ptr != '\0') {
+        /* Handle duplicate delimiter */
+        if (*ptr == '/' && *(ptr + 1) == '/') {
+            /*
+             * Snip this delimiter and skip, the next
+             * will be read and filename returned (if of course
+             * the index is reached).
+             */
+            *(ptr++) = '\0';
+            continue;
+        }
+
+        if (*ptr == '/') {
+            *(ptr++) = '\0';
+
+            /* Continue if index not reached */
+            if ((--idx) != 0) {
+                start_ptr = ptr;
+                continue;
+            }
+
+            /* Index has been reached, start_ptr contains name */
+            fname_len = strlen(start_ptr);
+            ret = dynalloc(fname_len + 1);
+
+            if (ret != NULL) {
+                memcpy(ret, start_ptr, fname_len + 1);
+            }
+            break;
+        }
+
+        ++ptr;
+    }
+
+    dynfree(path_tmp);
+    return ret;
+}
+
+/*
+ * Search for a path within a mountpoint.
+ *
+ * @mp: Mountpoint to search in.
+ * @path: Path to search for.
+ */
+static struct vnode *
+namei_mp_search(struct mount *mp, const char *path)
+{
+    struct vop_lookup_args lookup_args;
+    struct vnode *vp = mp->vp;
+    char *name;
+    int status;
+
+    for (size_t i = 1;; ++i) {
+        name = vfs_get_fname_at(path, i);
+        if (name == NULL)
+            break;
+
+        lookup_args.name = name;
+        lookup_args.dirvp = vp;
+        lookup_args.vpp = &vp;
+
+        status = vfs_vop_lookup(vp, &lookup_args);
+        dynfree(name);
+
+        if (status == 0)
+            return vp;
+    }
+
+    return NULL;
+}
+
 /*
  * Convert a path to a vnode.
  *
  * @ndp: Nameidata containing the path and resulting
  *       vnode.
- *
- * TODO: Add support for lookups with individual
- *       path components
  */
 int
 namei(struct nameidata *ndp)
 {
-    struct vnode *vp;
+    struct vnode *vp = NULL;
+    struct mount *mp;
     struct vop_lookup_args lookup_args;
     const char *path = ndp->path;
+    char *name;
     int status;
 
     if (path == NULL) {
@@ -66,6 +182,10 @@ namei(struct nameidata *ndp)
     }
 
     /*
+     * Start looking at the root vnode. If we can't find
+     * what we are looking for, we'll try traversing the
+     * mountlist.
+     *
      * Some filesystems (like initramfs) may only understand
      * full paths, so try passing it through.
      */
@@ -74,10 +194,33 @@ namei(struct nameidata *ndp)
     lookup_args.vpp = &vp;
     status = vfs_vop_lookup(lookup_args.dirvp, &lookup_args);
 
-    if (status != 0) {
-        return status;
+    /* Did we find it in the root */
+    if (status == 0) {
+        ndp->vp = vp;
+        return 0;
+    }
+
+    /* Look through the mountlist */
+    TAILQ_FOREACH(mp, &g_mountlist, mnt_list) {
+        /* If it is unamed, can't do anything */
+        if (mp->name == NULL)
+            continue;
+
+        lookup_args.dirvp = mp->vp;
+        name = vfs_get_fname_at(path, 0);
+
+        /* If the name matches, search within */
+        if (strcmp(mp->name, name) == 0)
+            vp = namei_mp_search(mp, path);
+
+        /* Did we find it at this mountpoint? */
+        if (vp != NULL) {
+            ndp->vp = vp;
+            return 0;
+        }
+
+        dynfree(name);
     }
 
-    ndp->vp = vp;
-    return 0;
+    return -ENOENT;
 }
-- 
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