library: standardize handling of cgroup, supgid

Some inconsistencies have emerged during development
of support for these relatively new proc_t fields.

For example, a PROC_FILLCGROUP flag (via file2strvec)
could return NULL in cgroup whereas PROC_EDITCGRPCVT
(via fill_cgroup_cvt) *almost* guaranteed a return
address (as is true for PROC_EDITCMDLCVT and cmdline).
But even PROC_EDITCGRPCVT could return NULL if the
kernel version was less than 2.6.24.  Then with NULL
ps would display a "-" while top would show "n/a".

And while unlikely, with the PROC_FILLSTATUS flag (via
status2proc) a NULL supgid address was theoretically
possible and both ps and top would then show "n/a".

This commit standardizes the following usage:
  . PROC_FILLSTATUS         (via status2proc)
      guarantees a valid supgid address
      representing either a true comma
      delimited list or "-"
  . PROC_FILLCGROUP  plus
    PROC_EDITCGRPCVT        (via fill_cgroup_cvt)
      guarantees a cgroup single vector
      representing either a true control
      group hierarchy or "-"

And as was true before, the following remains true:
    PROC_FILLCOM     or
    PROC_FILLARG            (via file2strvec)
      may return a NULL cmdline pointer
  . PROC_FILLCGROUP         (via file2strvec)
      may return a NULL cgroup pointer
  . PROC_FILLCOM     or
    PROC_FILLARG     plus
    PROC_EDITCMDLCVT        (via fill_cmdline_cvt)
      guarantees a cmdline single vector
      representing either a true command
      line or a bracketed program name
  . PROC_FILLSTATUS  plus
    PROC_FILLSUPGRP         (via supgrps_from_supgids)
      guarantees a valid supgrp address
      representing either a true comma
      delimited list or "-"

Signed-off-by: Jim Warner <james.warner@comcast.net>

diff --git a/proc/readproc.c b/proc/readproc.c
index 36658d9566c06d7c2215c397657c8e53b938fa1b..9ef587bfaa8976f8fcfad62b96980d3ae168f311 100644 (file)
--- a/proc/readproc.c
+++ b/proc/readproc.c
@@ -362,8 +362,7 @@ ENTER(0x220);
             for ( ; j; j--)
                 if (' '  == P->supgid[j])
                     P->supgid[j] = ',';
-        } else
-            P->supgid = xstrdup("-");
+        }
         continue;
     }
     case_CapBnd:
@@ -412,6 +411,9 @@ ENTER(0x220);
         P->tid  = Pid;
     }
 
+    if (!P->supgid)
+        P->supgid = xstrdup("-");
+
 LEAVE(0x220);
 }
 
@@ -793,8 +795,7 @@ static proc_t* simple_readproc(PROCTAB *restrict const PT, proc_t *restrict cons
     } else
         p->cmdline = NULL;
 
-    if ((flags & PROC_FILLCGROUP)               // read /proc/#/cgroup
-    && linux_version_code >= LINUX_VERSION(2,6,24)) {
+    if ((flags & PROC_FILLCGROUP)) {            // read /proc/#/cgroup
         if (flags & PROC_EDITCGRPCVT)
             fill_cgroup_cvt(path, p);
         else
@@ -903,8 +904,7 @@ static proc_t* simple_readtask(PROCTAB *restrict const PT, const proc_t *restric
         } else
             t->cmdline = NULL;
 
-        if ((flags & PROC_FILLCGROUP)                   // read /proc/#/task/#/cgroup
-        && linux_version_code >= LINUX_VERSION(2,6,24)) {
+        if ((flags & PROC_FILLCGROUP)) {                // read /proc/#/task/#/cgroup
             if (flags & PROC_EDITCGRPCVT)
                 fill_cgroup_cvt(path, t);
             else