On Tue, 2002-02-26 at 10:55, Swapnil Nagle wrote: > Petter Wahlman <petter@bluezone.no> wrote : > > > I found the answer to my question when I examined the vmalloc code. > > > > Could you please share your insight with the rest of us :) > > Swapnil. > > As I understand it, kernel pointers have redundant information because the last 8k of the 32bit virtual address space will never be returned by vmalloc(). This remaining space is reserved for an empty page, and a page for highmem PTE's (Strangely enough this is not in the x86 specific part of the kernel.) The "redundant" part of the kernel pointer is therefore used to return error codes, and the IS_ERR() checks for errors by comparing the pointer to 0xfffffc18. OTOH I did not understand why the author choose to check only the last 999 bytes of the pointer, or did a IMO, more readable AND operation. Petter Wahlman. -- Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ IRC Channel: irc.openprojects.net / #kernelnewbies Web Page: http://www.kernelnewbies.org/
