On Wed, 24 Oct 2012 16:27:30 +0400
Cyrill Gorcunov <[email protected]> wrote:
> During c/r sessions we've found that there is no way at the moment to
> fetch some VMA associated flags, such as mlock() and madvise().
>
> This leads us to a problem -- we don't know if we should call for mlock()
> and/or madvise() after restore on the vma area we're bringing back to
> life.
>
> This patch intorduces a new field into "smaps" output called VmFlags,
> where all set flags associated with the particular VMA is shown as two
> letter mnemonics.
>
> [ Strictly speaking for c/r we only need mlock/madvise bits but it has been
> said that providing just a few flags looks somehow inconsistent. So all
> flags are here now. ]
>
> This feature is made available on CONFIG_CHECKPOINT_RESTORE=n kernels, as
> other applications may start to use these fields.
>
> The data is encoded in a somewhat awkward two letters mnemonic form, to
> encourage userspace to be prepared for fields being added or removed in
> the future.
>
> ...
>
> + for_each_set_bit(i, &vma->vm_flags, BITS_PER_LONG) {
for_each_set_bit() seems to be rather sucky. Going back to
--- a/fs/proc/task_mmu.c~a-fix
+++ a/fs/proc/task_mmu.c
@@ -568,10 +568,11 @@ static void show_smap_vma_flags(struct s
size_t i;
seq_puts(m, "VmFlags: ");
- for_each_set_bit(i, &vma->vm_flags, BITS_PER_LONG) {
- seq_printf(m, "%c%c ",
- mnemonics[i][0],
- mnemonics[i][1]);
+ for (i = 0; i < BITS_PER_LONG; i++) {
+ if (vma->vm_flags & (1UL << i)) {
+ seq_printf(m, "%c%c ",
+ mnemonics[i][0], mnemonics[i][1]);
+ }
}
seq_putc(m, '\n');
}
saves 41 bytes. That's rather a lot for such a small code sequence.
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