hi all, I'm experimenting a bit with kiobuffers in 2.4.22-1.2174.nptlsmp [plain rpm kernel]

- I took arch/cris/drivers/examples/kiobuftest.c - compiled and insmod'd it - mknod /dev/kiobuftest c <major> 0 - run the user-mode test ktest.c (attached) [note: O_DIRECT in open is just a trie, it doesn't modify the result. It is there to test whether the O_DIRECT code path does something better...]

problem is that map_user_kiobuf() often puts 0's in maplist[i] for some/all i.

[root@xeone driver]# ./ktest buf=0xbf403008 addr=0xbf404000 len=8192 [root@xeone driver]# ./ktest buf=0xbf4c6008 addr=0xbf4c7000 len=8192 [root@xeone driver]# ./ktest buf=0xbf48f008 addr=0xbf490000 len=8192 [root@xeone driver]# dmesg nr_pages == 2 offset == 0 length == 8192 buf == 0xbf404000 page_add(maplist[0]) == 0xff8cd000 page_add(maplist[1]) == 0x00000000 nr_pages == 2 offset == 0 length == 8192 buf == 0xbf4c7000 page_add(maplist[0]) == 0x00000000 page_add(maplist[1]) == 0xff9cb000 nr_pages == 2 offset == 0 length == 8192 buf == 0xbf490000 page_add(maplist[0]) == 0xffa90000 page_add(maplist[1]) == 0x00000000

[root@xeone driver]# dd if=/dev/kiobuftest of=miao bs=8192 count=1 1+0 records in 1+0 records out [root@xeone driver]# dmesg |tail nr_pages == 2 offset == 0 length == 8192 buf == 0x09650000 page_add(maplist[0]) == 0xffa91000 page_add(maplist[1]) == 0x00000000

[root@xeone driver]# dd if=/dev/kiobuftest of=miao bs=$[2*8192] count=1 1+0 records in 1+0 records out [root@xeone driver]# dmesg |tail nr_pages == 4 offset == 0 length == 16384 buf == 0x08ee8000 page_add(maplist[0]) == 0xffaa9000 page_add(maplist[1]) == 0xff8d9000 page_add(maplist[2]) == 0x00000000 page_add(maplist[3]) == 0x00000000

so it seems that sometimes I get a kernel virtual address = 0...

it is strange as the code in memory.c:get_user_pages(), called by map_user_kiobuf(), has guards against it happening: if (pages) { pages[i] = get_page_map(map); /* FIXME: call the correct function, * depending on the type of the found page */ if (!pages[i]) goto bad_page; page_cache_get(pages[i]); }

seems like there is an error which is not propagated up to the caller of map_user_kiobuf()

I'm compiling a plain 2.4.25 + dprintk active to double check....

regards