lkml.org 
[lkml]   [2012]   [Jan]   [24]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectRe: [patch 2/4] [RFC] syscalls, x86: Add __NR_kcmp syscall v4
Date
Andrew Morton <akpm@linux-foundation.org> writes:


> <reads the code>
>
> Seems that it performs lookups only in the caller's PID namespace.
> Maybe this is appropriate but it should be described and justified in
> the changelog and in code comments, please. And in the forthcoming
> manpage ;)

Well pids should always and only be looked up in the callers pid
namespace. Any other behavior is broken. It is probably worth
a mention in a manpage but you should not need to justify using
abstractions as they were designed to be used.


>> +static int kcmp_ptr(long v1, long v2, int type)
>> +{
>> + long ret;
>> +
>> + ret = kptr_obfuscate(v1, type) - kptr_obfuscate(v2, type);
>> +
>> + return (ret < 0) | ((ret > 0) << 1);
>> +}
>> +
>> +#define KCMP_TASK_PTR(task1, task2, member, type) \
>> + kcmp_ptr((long)(task1)->member, \
>> + (long)(task2)->member, \
>> + type)
>> +
>> +#define KCMP_PTR(ptr1, ptr2, type) \
>> + kcmp_ptr((long)ptr1, (long)ptr2, type)
>
> ugh. This:
>
> static long kptr_obfuscate(void *p, enum you_forgot_to_name_the_enum type)
> {
> return ((long)p ^ cookies[type][0]) * cookies[type][1];
> }
>
> static int kcmp_task_pointers(void *task1, void *task2, size_t field_offset,
> enum you_forgot_to_name_the_enum type)
> {
> void **field1 = t1 + field_offset; /* points to a pointer in the task_struct */
> void **field2 = t1 + field_offset;
> long diff;
>
> diff = kptr_obfuscate(*field1, type) - kptr_obfuscate(*field2, type);
> return (diff < 0) | ((diff > 0) << 1);
> }
>
> ...
> ret = kcmp_task_pointers(task1, task2, offsetof(task_struct, mm),
> KCMP_VM);
> ...
>
> see? No nasty macros, it's type-correct and it uses only a single
> explicit typecast.

Seriously? Simply open coding the comparison would be better.

ret = kcmp_ptr(task1->files, task2->files, type);

All pointers are not encoded the same as void * pointers. Admittedly
the only case I can think of are function pointers on Itanium, but
what is a little wrong today can easily become a lot wrong tomorrow.

Making the kcmp_ptr arguments void * seems the way to go though.

Now there is one interesting case we are not handling properly.
If any of our pointers can be NULL which I think happens in the
file case we should return -EBADF instead of reporting two NULL
pointers point to the same object.

Eric


\
 
 \ /
  Last update: 2012-01-24 23:53    [from the cache]
©2003-2014 Jasper Spaans. Advertise on this site