From: Ben Greear <greearb@candelatech.com>
Date: Thu, 14 Feb 2002 19:10:20 -0700
When I make the copy from user call:
if ((ret = copy_from_user(&reqconf, arg, sizeof(reqconf)))) {
printk("ERROR: copy_from_user returned: %i, sizeof(reqconf): %i\n",
ret, sizeof(reqconf));
return ret;
}
I see this printed out:
ERROR: copy_from_user returned: 696, sizeof(reqconf): 696
Either:
1) 'arg' is a bogus userland pointer
or
2) 'arg' is a valid userland pointer, but someone has done a
set_fs(KERNEL_DS) so only kernel pointers are valid for user
copies.
A lot of the "32-bit userland on 64-bit kernel" compatability laters
work by doing #2. They munge the 32-bit user structures into kernel
side copies, and do set_fs(KERNEL_DS) and pass in the pointers to the
kernel copies to the real syscall then finally restore things back to
USER_DS.
copy_{to,from}_user always return, as you correctly noted, the amount
of data that could not be copied or "0" for success. That is why all
code does something like this:
err = 0;
if (copy_{to,from}_user(...))
err = -EFAULT;
I don't know where some people get the idea that copy_{to,from}_user
should return -EFAULT on failure. Maybe some port is buggy :-)
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This archive was generated by hypermail 2b29 : Fri Feb 15 2002 - 21:01:10 EST