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    SubjectRe: [PATCH] cpumask 5/10 rewrite cpumask.h - single bitmap based implementation
    William Lee Irwin III wrote:
    >> This is patently ridiculous. Make a compat_sched_getaffinity(), and
    >> likewise for whatever else is copying unsigned long arrays to userspace.

    On Fri, Jun 04, 2004 at 05:05:42PM -0700, Paul Jackson wrote:
    > My mind reading skills are failing me. At the risk of opening myself to
    > further ridicule, which part of what I wrote is patently ridiculous,
    > why, and how does that differ from whatever you had in mind when you
    > recommended doing "likewise"?

    Ridiculous == some bizarre for_each_cpu() loop doing put put_user() once
    for every bit of a cpumask_t.

    On Fri, Jun 04, 2004 at 05:05:42PM -0700, Paul Jackson wrote:
    > Putting your comments aside for a moment ...
    > We have here a bit of suckage. The kernel bitmaps/cpumasks are arrays
    > of unsigned long, with the low order long in the low order array slot,
    > and the bytes within the longs in natural byte-order for that arch. The
    > sched_setaffinity/sched_getaffinity calls in the kernel copy this stuff
    > directly to/from user space. This doesn't work so well for 32 bit tasks
    > on a 64 bit big-endian kernel. [Begin off-topic alert] The glibc
    > sched_setaffinity and sched_getaffinity calls forcibly truncate the size
    > of masks to some constant hardcoded size -- you have to use
    > __SYSCALL(__NR_set_mempolicy) and such to get the real syscall. This
    > doesn't work so well for kernels compiled with NR_CPUS larger than the
    > hardcoded glibc size. [End off-topic alert] This also doesn't provide
    > any help to other code needing to move binary masks across the
    > kernel/user boundary, such as the perfctr kernel extension that Mikael
    > Pettersson <> describes.

    Sounds like a glibc bug. It should probably dynamically detect
    sizeof(cpumask_t), except of course that the API it's stuck with for
    all time won't allow for dynamic allocation of the things.

    Except when I look at my glibc headers, it's 1024 bits. And they're not
    particularly recent glibc versions. SGI may need to get that bumped up,
    but I doubt many others do.

    On Fri, Jun 04, 2004 at 05:05:42PM -0700, Paul Jackson wrote:
    > I presume that it is too late to change the low level format of masks
    > that the sched_setaffinity/sched_getaffinity API support. I'd be
    > delighted to be wrong on this presumption. So there is need for a
    > compat variant of these calls, for use by 32 bit apps on 64 bit kernels.
    > My first reaction to Milton Miller's compat_sched_getaffinity patch
    > that Anton reminded us of is similar to Andrew's. I haven't had the
    > intestinal fortitude to study the matter closer yet. Before actually
    > reading the code, I would expect that all it had to handle was the
    > swapping of 32 bit halves of 64 bit longs on 64 bit big endian kernels,
    > such as I described in my discussion of a mythical BIT32X() macro,
    > earlier in this thread. I would not expect it to have to make such a
    > big deal of the special case of one word masks, as distinct from n word
    > masks, though I agree that a 32 bit app should be able to use a single
    > 32 bit word mask on a 64 bit kernel compiled with NR_CPUS <= 32.

    I thought something more like this would work, but haven't tried it.
    This wants a real copy_bitmap_to_user() helper unlike compat_set_fd_set().

    Index: irqaction-2.6.7-rc2/fs/compat.c
    --- irqaction-2.6.7-rc2.orig/fs/compat.c 2004-06-01 03:11:30.000000000 -0700
    +++ irqaction-2.6.7-rc2/fs/compat.c 2004-06-04 10:28:44.190035000 -0700
    @@ -40,6 +40,7 @@
    #include <linux/nfsd/nfsd.h>
    #include <linux/nfsd/syscall.h>
    #include <linux/personality.h>
    +#include <linux/cpu.h>

    #include <net/sock.h> /* siocdevprivate_ioctl */

    @@ -1394,6 +1395,31 @@
    return ret;

    +asmlinkage long compat_sched_getaffinity(compat_pid_t pid,
    + compat_uint_t len, compat_ulong_t __user *cpus)
    + cpumask_t affinity;
    + int ret = 0;
    + task_t *task;
    + if (len < sizeof(cpumask_t))
    + return -EINVAL;
    + if (!access_ok(VERIFY_WRITE, cpus, sizeof(cpumask_t)))
    + return -EFAULT;
    + lock_cpu_hotplug();
    + read_lock(&tasklist_lock);
    + if ((task = pid ? find_task_by_pid(pid) : current))
    + cpus_and(affinity, task->cpus_allowed, cpu_possible_map);
    + else
    + ret = -ESRCH;
    + read_unlock(&tasklist_lock);
    + unlock_cpu_hotplug();
    + if (ret)
    + return ret;
    + compat_set_fd_set(NR_CPUS, cpus, cpus_addr(affinity));
    + return sizeof(cpumask_t);
    #if defined(CONFIG_NFSD) || defined(CONFIG_NFSD_MODULE)
    /* Stuff for NFS server syscalls... */
    struct compat_nfsctl_svc {

    On Fri, Jun 04, 2004 at 05:05:42PM -0700, Paul Jackson wrote:
    > A key question, since it seems the perfctr stuff Mikael Pettersson
    > describes is on its way into the main stream kernel, is whether any
    > other kernel binary bitmap/cpumask API should use the same format as
    > used by the kernel sched_setaffinity and sched_getaffinity, or use a
    > more easily portable format - say an array of 32 bit words rather than
    > an array of unsigned longs. One could make impassioned pleas either
    > way. Having one kernel represent the same type in two different binary
    > formats is a bit of a botch. But then again, arrays of 32 bit words are
    > 'nicer'. And in fact, we already _have_ two formats required, since 32
    > bit apps on 64 bit end endian kernels necessarily see a different format
    > than their kernel uses natively -- indeed they use a format that is
    > essentially the same as perfctr is using now.

    This is trivial. Just like we needed ASCII marshalling, we need endian-
    correct 32/64-bit bitmap marshalling.

    On Fri, Jun 04, 2004 at 05:05:42PM -0700, Paul Jackson wrote:
    > My vote, already cast when I slid the 32 bit chunk ascii format past
    > y'all (it's amazing now, that I managed to do that ...) would be to
    > export the array of 32 bit words format from the kernel, in all calls
    > except the set/get affinity calls, where we have already cast the die
    > otherwise. I like what I understand Mikael is trying to do here.

    The only case where this is distinguished at all from copy_to_user() is
    64-bit bigendian with 32-bit userspace.

    On Fri, Jun 04, 2004 at 05:05:42PM -0700, Paul Jackson wrote:
    > In any case, I'd hope that any big/little endian distinctions could be
    > encapsulated in macros provided by include/linux/byteorder headers. I'd
    > hope that whichever one or two formats the kernel exported were
    > supported by conversion routines in bitmap.c and bitmap.h, and if
    > useful, also made available via the cpumask_t API. Once cpumask
    > routines were available to convert the perfctr format, then that would
    > be one less use of the infamous cpus_addr() macro. We should minimize
    > 'open coding' of the conversion routines outside of the bitmap routines,
    > which means look for the opportunity to move codes from both perfctr and
    > compat_sched_setaffinity into lib/bitmap.c.

    Index: irqaction-2.6.7-rc2/include/asm-generic/cpumask_array.h
    --- irqaction-2.6.7-rc2.orig/include/asm-generic/cpumask_array.h 2004-05-29 23:26:10.000000000 -0700
    +++ irqaction-2.6.7-rc2/include/asm-generic/cpumask_array.h 2004-06-04 18:29:36.984743000 -0700
    @@ -27,6 +27,8 @@
    #define first_cpu(map) find_first_bit((map).mask, NR_CPUS)
    #define next_cpu(cpu, map) find_next_bit((map).mask, NR_CPUS, cpu + 1)

    +#define cpus_to_u32_array(d, s) bitmap_to_u32_array(d, (s).mask, sizeof(cpumask_t))
    /* only ever use this for things that are _never_ used on large boxen */
    #define cpus_coerce(map) ((map).mask[0])
    #define cpus_promote(map) ({ cpumask_t __cpu_mask = CPU_MASK_NONE;\
    Index: irqaction-2.6.7-rc2/include/asm-generic/cpumask_arith.h
    --- irqaction-2.6.7-rc2.orig/include/asm-generic/cpumask_arith.h 2004-05-29 23:26:26.000000000 -0700
    +++ irqaction-2.6.7-rc2/include/asm-generic/cpumask_arith.h 2004-06-04 18:29:41.238097000 -0700
    @@ -38,6 +38,8 @@
    #define CPU_MASK_ALL (~((cpumask_t)0) >> (8*sizeof(cpumask_t) - NR_CPUS))
    #define CPU_MASK_NONE ((cpumask_t)0)

    +#define cpus_to_u32_array(d, s) bitmap_to_u32_array(d, &(s), sizeof(cpumask_t))
    /* only ever use this for things that are _never_ used on large boxen */
    #define cpus_coerce(map) ((unsigned long)(map))
    #define cpus_promote(map) ({ map; })
    Index: irqaction-2.6.7-rc2/include/asm-generic/cpumask_up.h
    --- irqaction-2.6.7-rc2.orig/include/asm-generic/cpumask_up.h 2004-05-29 23:25:55.000000000 -0700
    +++ irqaction-2.6.7-rc2/include/asm-generic/cpumask_up.h 2004-06-04 18:29:46.573286000 -0700
    @@ -40,6 +40,8 @@
    #define first_cpu(map) (cpus_coerce(map) ? 0 : 1)
    #define next_cpu(cpu, map) 1

    +#define cpus_to_u32_array(d, s) bitmap_to_u32_array(d, &(s), sizeof(cpumask_t))
    /* only ever use this for things that are _never_ used on large boxen */
    #define cpus_promote(map) \
    ({ \
    -- wli
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