vfs: embed struct filename inside of names_cache allocation if possible

In the common case where a name is much smaller than PATH_MAX, an extra
allocation for struct filename is unnecessary. Before allocating a
separate one, try to embed the struct filename inside the buffer first. If
it turns out that that's not long enough, then fall back to allocating a
separate struct filename and redoing the copy.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

diff --git a/fs/namei.c b/fs/namei.c
index 80b162b142f9e8c37a1bdc4024851d7e34a2d31b..d1895f30815670de8abd8a6c921443035c21a364 100644 (file)
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -119,40 +119,69 @@
  */
 void final_putname(struct filename *name)
 {
-       __putname(name->name);
-       kfree(name);
+       if (name->separate) {
+               __putname(name->name);
+               kfree(name);
+       } else {
+               __putname(name);
+       }
 }
 
+#define EMBEDDED_NAME_MAX      (PATH_MAX - sizeof(struct filename))
+
 static struct filename *
 getname_flags(const char __user *filename, int flags, int *empty)
 {
        struct filename *result, *err;
-       char *kname;
        int len;
+       long max;
+       char *kname;
 
        result = audit_reusename(filename);
        if (result)
                return result;
 
-       /* FIXME: create dedicated slabcache? */
-       result = kzalloc(sizeof(*result), GFP_KERNEL);
+       result = __getname();
        if (unlikely(!result))
                return ERR_PTR(-ENOMEM);
 
-       kname = __getname();
-       if (unlikely(!kname)) {
-               err = ERR_PTR(-ENOMEM);
-               goto error_free_name;
-       }
-
+       /*
+        * First, try to embed the struct filename inside the names_cache
+        * allocation
+        */
+       kname = (char *)result + sizeof(*result);
        result->name = kname;
-       result->uptr = filename;
-       len = strncpy_from_user(kname, filename, PATH_MAX);
+       result->separate = false;
+       max = EMBEDDED_NAME_MAX;
+
+recopy:
+       len = strncpy_from_user(kname, filename, max);
        if (unlikely(len < 0)) {
                err = ERR_PTR(len);
                goto error;
        }
 
+       /*
+        * Uh-oh. We have a name that's approaching PATH_MAX. Allocate a
+        * separate struct filename so we can dedicate the entire
+        * names_cache allocation for the pathname, and re-do the copy from
+        * userland.
+        */
+       if (len == EMBEDDED_NAME_MAX && max == EMBEDDED_NAME_MAX) {
+               kname = (char *)result;
+
+               result = kzalloc(sizeof(*result), GFP_KERNEL);
+               if (!result) {
+                       err = ERR_PTR(-ENOMEM);
+                       result = (struct filename *)kname;
+                       goto error;
+               }
+               result->name = kname;
+               result->separate = true;
+               max = PATH_MAX;
+               goto recopy;
+       }
+
        /* The empty path is special. */
        if (unlikely(!len)) {
                if (empty)
@@ -163,15 +192,15 @@ getname_flags(const char __user *filename, int flags, int *empty)
        }
 
        err = ERR_PTR(-ENAMETOOLONG);
-       if (likely(len < PATH_MAX)) {
-               audit_getname(result);
-               return result;
-       }
+       if (unlikely(len >= PATH_MAX))
+               goto error;
+
+       result->uptr = filename;
+       audit_getname(result);
+       return result;
 
 error:
-       __putname(kname);
-error_free_name:
-       kfree(result);
+       final_putname(result);
        return err;
 }
 

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 4aa7160a51cecb49d6269d7fb8ea967c8102b502..65fbf571023f6f8f2ffb48f686e7fc33fab023c7 100644 (file)
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2201,6 +2201,7 @@ struct filename {
        const char              *name;  /* pointer to actual string */
        const __user char       *uptr;  /* original userland pointer */
        struct audit_names      *aname;
+       bool                    separate; /* should "name" be freed? */
 };
 
 extern int do_truncate(struct dentry *, loff_t start, unsigned int time_attrs,