library: expanded to provide for the 'executable path'

This patch is the first of three implementing a newlib
branch version of that Jan Rybar master merge request.

With this series we'll ultimately extend 'EXE' support
to both ps and top (plus, everyone else who wants it).

Reference(s):
. master branch merge request
https://gitlab.com/procps-ng/procps/merge_requests/66

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

proc/pids.c

@@ -155,6 +155,7 @@ STR_set(CMDLINE,                   cmdline)
 VEC_set(CMDLINE_V,                 cmdline_v)
 STR_set(ENVIRON,                   environ)
 VEC_set(ENVIRON_V,                 environ_v)
+STR_set(EXE,                       exe)
 REG_set(EXIT_SIGNAL,      s_int,   exit_signal)
 REG_set(FLAGS,            ul_int,  flags)
 REG_set(FLT_MAJ,          ul_int,  maj_flt)
@@ -343,6 +344,7 @@ srtDECL(noop) {
 // ___ Controlling Table ||||||||||||||||||||||||||||||||||||||||||||||||||||||
 
 #define f_either   PROC_SPARE_1        // either status or stat (favor stat)
+#define f_exe      PROC_FILL_EXE
 #define f_grp      PROC_FILLGRP
 #define f_login    PROC_FILL_LUID
 #define f_lxc      PROC_FILL_LXC
@@ -406,6 +408,7 @@ static struct {
     { RS(CMDLINE_V),         v_arg,      FF(strv),  QS(strv),      0,        TS(strv)    },
     { RS(ENVIRON),           x_environ,  FF(str),   QS(str),       0,        TS(str)     },
     { RS(ENVIRON_V),         v_env,      FF(strv),  QS(strv),      0,        TS(strv)    },
+    { RS(EXE),               f_exe,      FF(str),   QS(str),       0,        TS(str)     },
     { RS(EXIT_SIGNAL),       f_stat,     NULL,      QS(s_int),     0,        TS(s_int)   },
     { RS(FLAGS),             f_stat,     NULL,      QS(ul_int),    0,        TS(ul_int)  },
     { RS(FLT_MAJ),           f_stat,     NULL,      QS(ul_int),    0,        TS(ul_int)  },

proc/pids.h

@@ -43,6 +43,7 @@ enum pids_item {
     PIDS_CMDLINE_V,         //    strv
     PIDS_ENVIRON,           //     str
     PIDS_ENVIRON_V,         //    strv
+    PIDS_EXE,               //     str
     PIDS_EXIT_SIGNAL,       //   s_int
     PIDS_FLAGS,             //  ul_int
     PIDS_FLT_MAJ,           //  ul_int

proc/readproc.c

@@ -90,16 +90,15 @@ static int task_dir_missing;
 // free any additional dynamically acquired storage associated with a proc_t
 // ( and if it's to be reused, refresh it otherwise destroy it )
 static inline void free_acquired (proc_t *p, int reuse) {
-    if (p->environ)   free((void*)p->environ);
-    if (p->cmdline)   free((void*)p->cmdline);
     if (p->cgname)    free((void*)p->cgname);
     if (p->cgroup)    free((void*)p->cgroup);
-    if (p->environ_v) free((void*)*p->environ_v);
-    if (p->cmdline_v) free((void*)*p->cmdline_v);
     if (p->cgroup_v)  free((void*)*p->cgroup_v);
-    if (p->supgid)    free(p->supgid);
-    if (p->supgrp)    free(p->supgrp);
     if (p->cmd)       free(p->cmd);
+    if (p->cmdline)   free((void*)p->cmdline);
+    if (p->cmdline_v) free((void*)*p->cmdline_v);
+    if (p->environ)   free((void*)p->environ);
+    if (p->environ_v) free((void*)*p->environ_v);
+    if (p->exe)       free(p->exe);
     if (p->sd_mach)   free(p->sd_mach);
     if (p->sd_ouid)   free(p->sd_ouid);
     if (p->sd_seat)   free(p->sd_seat);
@@ -107,6 +106,8 @@ static inline void free_acquired (proc_t *p, int reuse) {
     if (p->sd_slice)  free(p->sd_slice);
     if (p->sd_unit)   free(p->sd_unit);
     if (p->sd_uunit)  free(p->sd_uunit);
+    if (p->supgid)    free(p->supgid);
+    if (p->supgrp)    free(p->supgrp);
 
     memset(p, reuse ? '\0' : '\xff', sizeof(*p));
 }
@@ -982,6 +983,20 @@ static int login_uid (const char *path) {
 }
 
 
+static char *readlink_exe (const char *path){
+    char buf[PROCPATHLEN];
+    int in;
+
+    snprintf(buf, sizeof(buf), "%s/exe", path);
+    in = (int)readlink(buf, dst_buffer, MAX_BUFSZ-1);
+    if (in > 0) {
+        dst_buffer[in] = '\0';
+        return strdup(dst_buffer);
+    }
+    return strdup("-");
+}
+
+
 ///////////////////////////////////////////////////////////////////////
 
 /* These are some nice GNU C expression subscope "inline" functions.
@@ -1106,6 +1121,9 @@ static proc_t* simple_readproc(PROCTAB *restrict const PT, proc_t *restrict cons
     if (flags & PROC_FILL_LUID)                 // value the login user id
         p->luid = login_uid(path);
 
+    if (flags & PROC_FILL_EXE)
+        p->exe = readlink_exe(path);
+
     if (rc == 0) return p;
     errno = ENOMEM;
 next_proc:
@@ -1193,6 +1211,9 @@ static proc_t* simple_readtask(PROCTAB *restrict const PT, const proc_t *restric
 
     if (flags & PROC_FILLSYSTEMD)                   // get sd-login.h stuff
         rc += sd2proc(t);
+
+    if (flags & PROC_FILL_EXE)
+        t->exe = readlink_exe(path);
 #ifdef FALSE_THREADS
     }
 #endif

proc/readproc.h

@@ -162,7 +162,8 @@ typedef struct proc_t {
         *sd_unit,       // n/a             systemd system unit id
         *sd_uunit;      // n/a             systemd user unit id
     char
-        *lxcname;       // n/a             lxc container name
+        *lxcname,       // n/a             lxc container name
+        *exe;           // exe             executable path + name
     int
         luid;           // loginuid        user id at login
 } proc_t;
@@ -224,6 +225,7 @@ typedef struct PROCTAB {
 #define PROC_FILLSYSTEMD    0x80000 // fill in proc_t systemd information
 #define PROC_FILL_LXC      0x800000 // fill in proc_t lxcname, if possible
 #define PROC_FILL_LUID     0x400000 // fill in proc_t luid (login user id)
+#define PROC_FILL_EXE      0x200000 // fill in proc_t exe path + pgm name
 
 #define PROC_LOOSE_TASKS     0x2000 // treat threads as if they were processes