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Commit f773f32d authored by Rasmus Villemoes's avatar Rasmus Villemoes Committed by Linus Torvalds
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lib/kobject.c: use kvasprintf_const for formatting ->name 



Sometimes kobject_set_name_vargs is called with a format string conaining
no %, or a format string of precisely "%s", where the single vararg
happens to point to .rodata.  kvasprintf_const detects these cases for us
and returns a copy of that pointer instead of duplicating the string, thus
saving some run-time memory.  Otherwise, it falls back to kvasprintf.  We
just need to always deallocate ->name using kfree_const.

Unfortunately, the dance we need to do to perform the '/' -> '!'
sanitization makes the resulting code rather ugly.

I instrumented kstrdup_const to provide some statistics on the memory
saved, and for me this gave an additional ~14KB after boot (306KB was
already saved; this patch bumped that to 320KB).  I have
KMALLOC_SHIFT_LOW==3, and since 80% of the kvasprintf_const hits were
satisfied by an 8-byte allocation, the 14K would roughly be quadrupled
when KMALLOC_SHIFT_LOW==5.  Whether these numbers are sufficient to
justify the ugliness I'll leave to others to decide.

Signed-off-by: default avatarRasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Greg KH <greg@kroah.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 0a9df786

lib/kobject.c

+22 −8
Original line number Diff line number Diff line
@@ -257,18 +257,32 @@ static int kobject_add_internal(struct kobject *kobj) 
int kobject_set_name_vargs(struct kobject *kobj, const char *fmt,

				  va_list vargs)

{

	char *s;

	const char *s;



	if (kobj->name && !fmt)

		return 0;



	s = kvasprintf(GFP_KERNEL, fmt, vargs);

	s = kvasprintf_const(GFP_KERNEL, fmt, vargs);

	if (!s)

		return -ENOMEM;



	/* ewww... some of these buggers have '/' in the name ... */

	strreplace(s, '/', '!');

	kfree(kobj->name);

	/*

	 * ewww... some of these buggers have '/' in the name ... If

	 * that's the case, we need to make sure we have an actual

	 * allocated copy to modify, since kvasprintf_const may have

	 * returned something from .rodata.

	 */

	if (strchr(s, '/')) {

		char *t;



		t = kstrdup(s, GFP_KERNEL);

		kfree_const(s);

		if (!t)

			return -ENOMEM;

		strreplace(t, '/', '!');

		s = t;

	}

	kfree_const(kobj->name);

	kobj->name = s;



	return 0;
@@ -466,7 +480,7 @@ int kobject_rename(struct kobject *kobj, const char *new_name) 
	envp[0] = devpath_string;

	envp[1] = NULL;



	name = dup_name = kstrdup(new_name, GFP_KERNEL);

	name = dup_name = kstrdup_const(new_name, GFP_KERNEL);

	if (!name) {

		error = -ENOMEM;

		goto out;
@@ -486,7 +500,7 @@ int kobject_rename(struct kobject *kobj, const char *new_name) 
	kobject_uevent_env(kobj, KOBJ_MOVE, envp);



out:

	kfree(dup_name);

	kfree_const(dup_name);

	kfree(devpath_string);

	kfree(devpath);

	kobject_put(kobj);
@@ -634,7 +648,7 @@ static void kobject_cleanup(struct kobject *kobj) 
	/* free name if we allocated it */

	if (name) {

		pr_debug("kobject: '%s': free name\n", name);

		kfree(name);

		kfree_const(name);

	}

}