Treat NFS ESTALE fds as unlinked for +L selection

On  NFS clients, a file can be deleted on the server while still
referenced by an open fd on the client. In such cases, stat(2)/lstat(2)
on /proc/<pid>/fd/<n> may fail with ESTALE ("Stale file handle").

lsof's +L selection is commonly used to find open-but-unlinked files,
but ESTALE fds were not selectable. Record per-fd errno from statsafely()
/ lstatsafely() and, when +L selection is enabled (SELNLINK), mark the
file as matching and annotate NAME with " (STALE)".

This helps identify NFS open-but-deleted/stale file handles using existing
+L workflows without introducing new command-line options.

Signed-off-by: Jeff Xie <xiehuan09@gmail.com>

Author: Jeff Xie

lib/dialects/linux/dproc.c

@@ -917,6 +917,8 @@ static int process_id(struct lsof_context *ctx, /* context */
     static int pathil = 0;
     char *rest;
     int txts = 0;
+    int enss_fd = 0;
+    int enls_fd = 0;
 
 #if defined(HASSELINUX)
     cntxlist_t *cntxp;
@@ -1206,13 +1208,15 @@ static int process_id(struct lsof_context *ctx, /* context */
             } else {
                 if (HasNFS) {
                     if (lstatsafely(ctx, path, &lsb)) {
+                        enls_fd = errno;
                         (void)statEx(ctx, pbuf, &lsb, &ls);
                         enls = errno;
                     } else {
                         enls = 0;
                         ls = SB_ALL;
                     }
                     if (statsafely(ctx, path, &sb)) {
+                        enss_fd = errno;
                         (void)statEx(ctx, pbuf, &sb, &ss);
                         enss = errno;
                     } else {
@@ -1353,6 +1357,12 @@ static int process_id(struct lsof_context *ctx, /* context */
                     enter_nm(ctx, rest);
                 }
 
+               if ((Selflags & SELNLINK) &&
+                   (enss_fd == ESTALE || enls_fd == ESTALE)) {
+                   Lf->sf |= SELNLINK;
+                   (void)add_nma(ctx, " (STALE)", 8);
+                }
+
                 if (Lf->sf)
                     link_lfile(ctx);
             }