It would be possible to optimize this one slightly:
replace
lock_kernel();
dentry = namei(filename);
with
{
char *name;
name = getname(filename);
if(IS_ERR(name))
return PTR_ERR(name);
lock_kernel();
dentry = lookup_dentry(name,);
putname(name);
}
[ or a new "lock_and_namei()" function]
getname() is SMP safe, and many functions call it before lock_kernel()
[sys_rename(), sys_link()].
I made a quick benchmark (for(;;) stat("/bin")), and the kernel spends
30 % in get_name(), strncpy_from_user, rmqueue and __alloc_pages() [but
debugging options enabled, 2.2.12-20smp spends ~ 15 % in these
functions]
>
> 172 146 190 159 667 sys_open+132 0xc026b7e4
>
getname() should be moved before lock_kernel(), but I doubt that this
will have a noticeable effect.
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