find: make -delete honour the -ignore_readdir_race option

* find/pred.c (pred_delete): Return true when the -ignore_readdir_race
option is active and unlinkat() came back with ENOENT.
* doc/find.texi (Option -ignore_readdir_race): Document the change.
(Action -delete): Likewise.
* find/find.1: Likewise.
* NEWS (Bug Fixes): Mention the fix.

For now, it seems a bit hard to add a proper test for this,
so the following shell snippet demonstrates the race:

  $ seq 10 | xargs touch
  $ env time -f 'find exit status: %x\nfind time: %e' \
      find -ignore_readdir_race -type f \
        -delete \
        -exec sh -c 'sleep $(basename {})' \; \
        -printf 'find deleted: %p\n' \
        & \
    sleep 20; \
    seq 10 | xargs rm -fv; \
    wait $!

Reported by Alexander Golubev in
https://savannah.gnu.org/bugs/?52981

NEWS

@@ -54,6 +54,10 @@ Some minor documentation improvements are listed in "Bug Fixes" below.
 
 ** Bug Fixes
 
+#52981: find: the '-delete' action no longer complains about disappeared files
+        when the '-ignore_readdir_race' option is given, too.  That action will
+        also returns true in such a case now.
+
 #52220: 'find -D' without any further argument no longer crashes.
         Bug present since the implementation of -D in FINDUTILS_4_3_1-1.
 

doc/find.texi

@@ -1424,7 +1424,15 @@ gives a significant increase in search speed.
 If a file disappears after its name has been read from a directory but
 before @code{find} gets around to examining the file with @code{stat},
 don't issue an error message.  If you don't specify this option, an
-error message will be issued.  This option can be useful in system
+error message will be issued.
+
+Furthermore, @code{find} with the @samp{-ignore_readdir_race} option
+will ignore errors of the @samp{-delete} action in the case the file
+has disappeared since the parent directory was read: it will not output
+an error diagnostic, and the return code of the @samp{-delete} action
+will be true.
+
+This option can be useful in system
 scripts (cron scripts, for example) that examine areas of the
 filesystem that change frequently (mail queues, temporary directories,
 and so forth), because this scenario is common for those sorts of
@@ -2787,6 +2795,11 @@ explicitly.
 
 If @samp{-delete} fails, @code{find}'s exit status will be nonzero
 (when it eventually exits).
+
+Together with the @samp{-ignore_readdir_race} option, @code{find} will
+ignore errors of the @samp{-delete} action in the case the file has disappeared
+since the parent directory was read: it will not output an error diagnostic, and
+the return code of the @samp{-delete} action will be true.
 @end deffn
 
 @node Adding Tests

find/find.1

@@ -495,6 +495,17 @@ this option on and part of it with this option off
 (if you need to do that, you will need to issue two \fBfind\fR commands
 instead, one with the option and one without it).
 
+Furthermore,
+.B find
+with the
+.B \-ignore_readdir_race
+option will ignore errors of the
+.B \-delete
+action in the case the file has disappeared since the parent directory was read:
+it will not output an error diagnostic, and the return code of the
+.B \-delete
+action will be true.
+
 .IP "\-maxdepth \fIlevels\fR"
 Descend at most \fIlevels\fR (a non-negative integer) levels of
 directories below the starting-points.
@@ -1087,6 +1098,17 @@ and
 .B \-delete
 together.
 
+Together with the
+.B \-ignore_readdir_race
+option,
+.B find
+will ignore errors of the
+.B \-delete
+action in the case the file has disappeared since the parent directory was
+read: it will not output an error diagnostic, and the return code of the
+.B \-delete
+action will be true.
+
 .IP "\-exec \fIcommand\fR ;"
 Execute
 .IR command ;

find/pred.c

@@ -316,6 +316,12 @@ pred_delete (const char *pathname, struct stat *stat_buf, struct predicate *pred
 	}
       else
 	{
+	  if (ENOENT == errno && options.ignore_readdir_race)
+	    {
+	      /* Ignore unlink() error for vanished files.  */
+	      errno = 0;
+	      return true;
+	    }
 	  if (EISDIR == errno)
 	    {
 	      if ((flags & AT_REMOVEDIR) == 0)