[PATCH v7 19/49] vfs: embed getname_info inside of names_cache allocation if possible

Jeff Layton
2012-10-02T00:17:32Z

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

Signed-off-by: Jeff Layton <jlayton@redhat.com>
---
fs/namei.c | 69 ++++++++++++++++++++++++++++++++++++++----------------
include/linux/fs.h | 1 +
2 files changed, 50 insertions(+), 20 deletions(-)

diff --git a/fs/namei.c b/fs/namei.c
index 5e2f5ae..48cb4aa 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -119,40 +119,69 @@
*/
void final_putname(struct getname_info *ginfo)
{
- __putname(ginfo->name);
- kfree(ginfo);
+ if (ginfo->separate) {
+ __putname(ginfo->name);
+ kfree(ginfo);
+ } else {
+ __putname(ginfo);
+ }
}

+#define EMBEDDED_NAME_MAX (PATH_MAX - sizeof(struct getname_info))
+
static struct getname_info *
getname_flags(const char __user *filename, int flags, int *empty)
{
struct getname_info *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_ginfo;
- }
-
+ /*
+ * First, try to embed the getname_info 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 getname_info struct 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 getname_info *)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_ginfo:
- kfree(result);
+ final_putname(result);
return err;
}

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 4ce38f2..a3c2c17 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2194,6 +2194,7 @@ struct getname_info {
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,
--
1.7.11.4