Hi,
Could someone explain to me what was the intent of the following
piece of code (extracted from linux-2.3.35 in fs/buffer.c) ?
int block_write_zero_range(struct inode *inode, struct page *page,
unsigned zerofrom, unsigned from, unsigned to,
const char * buf)
{
....
/*
* Now we can copy the data.
*/
if (zerofrom < from)
memset(kaddr+zerofrom, 0, from-zerofrom);
if (from < to)
>>>> err = copy_from_user(kaddr+from, buf, to-from);
if (to < zeroto)
memset(kaddr+to, 0, zeroto-to);
else
zeroto = to;
>>>>> if (err < 0)
goto out;
copy_from_user() always returns something that is >= 0 so the test
err < 0 is never taken. In this case, isn't the use of err for
copy_from_user() kind of confusing ?
I understand that POSIX does not define the behavior of write when
you have a wild pointer. That's the behavior that you get here:
write never fails because buf is invalid. I have seen systems where
the behavior is to return EFAULT though.
Any comments ?
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| Ste'phane ERANIAN | Email eranian@hpl.hp.com |
| Hewlett-Packard Laboratories | |
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