procfs: add VmFlags field in smaps output

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.

[a.p.zijlstra@chello.nl: props to use for_each_set_bit]
[sfr@canb.auug.org.au: props to use array instead of struct]
[akpm@linux-foundation.org: overall redesign and simplification]
[akpm@linux-foundation.org: remove unneeded braces per sfr, avoid using bloaty for_each_set_bit()]
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Cc: Pavel Emelyanov <xemul@parallels.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 53 insertions, 0 deletions

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 48775628abbf..448455b7fd91 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -526,6 +526,57 @@ static int smaps_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
         return 0;
 }
 
+static void show_smap_vma_flags(struct seq_file *m, struct vm_area_struct *vma)
+{
+        /*
+         * Don't forget to update Documentation/ on changes.
+         */
+        static const char mnemonics[BITS_PER_LONG][2] = {
+                /*
+                 * In case if we meet a flag we don't know about.
+                 */
+                [0 ... (BITS_PER_LONG-1)] = "??",
+
+                [ilog2(VM_READ)]        = "rd",
+                [ilog2(VM_WRITE)]       = "wr",
+                [ilog2(VM_EXEC)]        = "ex",
+                [ilog2(VM_SHARED)]      = "sh",
+                [ilog2(VM_MAYREAD)]     = "mr",
+                [ilog2(VM_MAYWRITE)]    = "mw",
+                [ilog2(VM_MAYEXEC)]     = "me",
+                [ilog2(VM_MAYSHARE)]    = "ms",
+                [ilog2(VM_GROWSDOWN)]   = "gd",
+                [ilog2(VM_PFNMAP)]      = "pf",
+                [ilog2(VM_DENYWRITE)]   = "dw",
+                [ilog2(VM_LOCKED)]      = "lo",
+                [ilog2(VM_IO)]          = "io",
+                [ilog2(VM_SEQ_READ)]    = "sr",
+                [ilog2(VM_RAND_READ)]   = "rr",
+                [ilog2(VM_DONTCOPY)]    = "dc",
+                [ilog2(VM_DONTEXPAND)]  = "de",
+                [ilog2(VM_ACCOUNT)]     = "ac",
+                [ilog2(VM_NORESERVE)]   = "nr",
+                [ilog2(VM_HUGETLB)]     = "ht",
+                [ilog2(VM_NONLINEAR)]   = "nl",
+                [ilog2(VM_ARCH_1)]      = "ar",
+                [ilog2(VM_DONTDUMP)]    = "dd",
+                [ilog2(VM_MIXEDMAP)]    = "mm",
+                [ilog2(VM_HUGEPAGE)]    = "hg",
+                [ilog2(VM_NOHUGEPAGE)]  = "nh",
+                [ilog2(VM_MERGEABLE)]   = "mg",
+        };
+        size_t i;
+
+        seq_puts(m, "VmFlags: ");
+        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');
+}
+
 static int show_smap(struct seq_file *m, void *v, int is_pid)
 {
         struct proc_maps_private *priv = m->private;
@@ -581,6 +632,8 @@ static int show_smap(struct seq_file *m, void *v, int is_pid)
                 seq_printf(m, "Nonlinear:      %8lu kB\n",
                                 mss.nonlinear >> 10);
 
+        show_smap_vma_flags(m, vma);
+
         if (m->count < m->size)  /* vma is copied successfully */
                 m->version = (vma != get_gate_vma(task->mm))
                         ? vma->vm_start : 0;