From: Paul Eggert <eggert@cs.ucla.edu>
Date: Sat, 4 Mar 2023 21:40:28 +0000 (-0800)
Subject: split: tune for when creating output files
X-Git-Tag: v9.2~23
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=8022874d1242f3b094b6bd001e83845e289d2bb1;p=thirdparty%2Fcoreutils.git

split: tune for when creating output files

* src/split.c (create): Avoid fstat + ftruncate in the usual case
where the output file does not already exist, by trying
to create it with O_EXCL first.  This costs a failed open
in the unusual case where the output file already exists,
but that’s OK.
---

diff --git a/src/split.c b/src/split.c
index 8550ef4420..cc581b6c65 100644
--- a/src/split.c
+++ b/src/split.c
@@ -459,7 +459,11 @@ create (char const *name)
       if (verbose)
         fprintf (stdout, _("creating file %s\n"), quoteaf (name));
 
-      int fd = open (name, O_WRONLY | O_CREAT | O_BINARY, MODE_RW_UGO);
+      int oflags = O_WRONLY | O_CREAT | O_BINARY;
+      int fd = open (name, oflags | O_EXCL, MODE_RW_UGO);
+      if (0 <= fd || errno != EEXIST)
+        return fd;
+      fd = open (name, oflags, MODE_RW_UGO);
       if (fd < 0)
         return fd;
       struct stat out_stat_buf;
@@ -468,8 +472,10 @@ create (char const *name)
       if (SAME_INODE (in_stat_buf, out_stat_buf))
         die (EXIT_FAILURE, 0, _("%s would overwrite input; aborting"),
              quoteaf (name));
-      if (ftruncate (fd, 0) != 0
-          && (S_ISREG (out_stat_buf.st_mode) || S_TYPEISSHM (&out_stat_buf)))
+      bool regularish
+        = S_ISREG (out_stat_buf.st_mode) || S_TYPEISSHM (&out_stat_buf);
+      if (! (regularish && out_stat_buf.st_size == 0)
+          && ftruncate (fd, 0) < 0 && regularish)
         die (EXIT_FAILURE, errno, _("%s: error truncating"), quotef (name));
 
       return fd;