Partial backport of the sendfile removal.  This backport only
updates nscd/netgroupcache.c, to avoid future conflicts.

commit 8c78faa9ef5c6cae455739f162e4b9d690e32eca
Author: Adhemerval Zanella <adhemerval.zanella@linaro.org>
Date:   Wed May 16 10:51:15 2018 -0300

    Fix concurrent changes on nscd aware files (BZ #23178)
    
    As indicated by BZ#23178, concurrent access on some files read by nscd
    may result non expected data send through service requisition.  This is
    due 'sendfile' Linux implementation where for sockets with zero-copy
    support, callers must ensure the transferred portions of the the file
    reffered by input file descriptor remain unmodified until the reader
    on the other end of socket has consumed the transferred data.
    
    I could not find any explicit documentation stating this behaviour on
    Linux kernel documentation.  However man-pages sendfile entry [1] states
    in NOTES the aforementioned remark.  It was initially pushed on man-pages
    with an explicit testcase [2] that shows changing the file used in
    'sendfile' call prior the socket input data consumption results in
    previous data being lost.
    
    From commit message it stated on tested Linux version (3.15) only TCP
    socket showed this issues, however on recent kernels (4.4) I noticed the
    same behaviour for local sockets as well.
    
    Since sendfile on HURD is a read/write operation and the underlying
    issue on Linux, the straightforward fix is just remove sendfile use
    altogether.  I am really skeptical it is hitting some hotstop (there
    are indication over internet that sendfile is helpfull only for large
    files, more than 10kb) here to justify that extra code complexity or
    to pursuit other possible fix (through memory or file locks for
    instance, which I am not sure it is doable).
    
    Checked on x86_64-linux-gnu.
    
            [BZ #23178]
            * nscd/nscd-client.h (sendfileall): Remove prototype.
            * nscd/connections.c [HAVE_SENDFILE] (sendfileall): Remove function.
            (handle_request): Use writeall instead of sendfileall.
            * nscd/aicache.c (addhstaiX): Likewise.
            * nscd/grpcache.c (cache_addgr): Likewise.
            * nscd/hstcache.c (cache_addhst): Likewise.
            * nscd/initgrcache.c (addinitgroupsX): Likewise.
            * nscd/netgroupcache.c (addgetnetgrentX, addinnetgrX): Likewise.
            * nscd/pwdcache.c (cache_addpw): Likewise.
            * nscd/servicescache.c (cache_addserv): Likewise.
            * sysdeps/unix/sysv/linux/Makefile [$(subdir) == nscd]
            (sysdep-CFLAGS): Remove -DHAVE_SENDFILE.
            * sysdeps/unix/sysv/linux/kernel-features.h (__ASSUME_SENDFILE):
            Remove define.
    
    [1] http://man7.org/linux/man-pages/man2/sendfile.2.html
    [2] https://github.com/mkerrisk/man-pages/commit/7b6a3299776b5c1c4f169a591434a855d50c68b4#diff-efd6af3a70f0f07c578e85b51e83b3c3

diff --git a/nscd/netgroupcache.c b/nscd/netgroupcache.c
index 4fce79283a9badb3..7ee0c284ed58d1e3 100644
--- a/nscd/netgroupcache.c
+++ b/nscd/netgroupcache.c
@@ -415,33 +415,7 @@ addgetnetgrentX (struct database_dyn *db, int fd, request_header *req,
 	 since while inserting this thread might block and so would
 	 unnecessarily let the receiver wait.  */
     writeout:
-#ifdef HAVE_SENDFILE
-      if (__builtin_expect (db->mmap_used, 1) && cacheable)
-	{
-	  assert (db->wr_fd != -1);
-	  assert ((char *) &dataset->resp > (char *) db->data);
-	  assert ((char *) dataset - (char *) db->head + total
-		  <= (sizeof (struct database_pers_head)
-		      + db->head->module * sizeof (ref_t)
-		      + db->head->data_size));
-# ifndef __ASSUME_SENDFILE
-	  ssize_t written =
-# endif
-	    sendfileall (fd, db->wr_fd, (char *) &dataset->resp
-			 - (char *) db->head, dataset->head.recsize);
-# ifndef __ASSUME_SENDFILE
-	  if (written == -1 && errno == ENOSYS)
-	    goto use_write;
-# endif
-	}
-      else
-#endif
-	{
-#if defined HAVE_SENDFILE && !defined __ASSUME_SENDFILE
-	use_write:
-#endif
-	  writeall (fd, &dataset->resp, dataset->head.recsize);
-	}
+      writeall (fd, &dataset->resp, dataset->head.recsize);
     }
 
   if (cacheable)
@@ -596,36 +570,9 @@ addinnetgrX (struct database_dyn *db, int fd, request_header *req,
       /* We write the dataset before inserting it to the database
 	 since while inserting this thread might block and so would
 	 unnecessarily let the receiver wait.  */
-       assert (fd != -1);
+      assert (fd != -1);
 
-#ifdef HAVE_SENDFILE
-      if (__builtin_expect (db->mmap_used, 1) && cacheable)
-	{
-	  assert (db->wr_fd != -1);
-	  assert ((char *) &dataset->resp > (char *) db->data);
-	  assert ((char *) dataset - (char *) db->head + sizeof (*dataset)
-		  <= (sizeof (struct database_pers_head)
-		      + db->head->module * sizeof (ref_t)
-		      + db->head->data_size));
-# ifndef __ASSUME_SENDFILE
-	  ssize_t written =
-# endif
-	    sendfileall (fd, db->wr_fd,
-			 (char *) &dataset->resp - (char *) db->head,
-			 sizeof (innetgroup_response_header));
-# ifndef __ASSUME_SENDFILE
-	  if (written == -1 && errno == ENOSYS)
-	    goto use_write;
-# endif
-	}
-      else
-#endif
-	{
-#if defined HAVE_SENDFILE && !defined __ASSUME_SENDFILE
-	use_write:
-#endif
-	  writeall (fd, &dataset->resp, sizeof (innetgroup_response_header));
-	}
+      writeall (fd, &dataset->resp, sizeof (innetgroup_response_header));
     }
 
   if (cacheable)