bug#13352: [PATCH] cp: ignore EEXIST errors from mkdir

[Mike Frysinger]

If you're copying multiple source trees into a single destination in
parallel (which have overlapping dirs, but not files), you can easily
hit a race condition.

This can crop up more generally if you're running multiple installs
from different build directories in parallel.  You don't get as much
of a speed up due to the parallel I/O, but you do from processing all
the build scripts.

Simple test to reproduce:
        mkdir -p in/`printf %s/ {a..z} {0..10}`
        (rm -rf out; for ((i=0;i<100;++i)); do cp -pPR in out & :; done)

* src/cp.c (make_dir_parents_private): Ignore EEXIST from mkdir.
---
 src/cp.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/src/cp.c b/src/cp.c
index 625ea0b..b9dff18 100644
--- a/src/cp.c
+++ b/src/cp.c
@@ -473,9 +473,15 @@ make_dir_parents_private (char const *const_dir, size_t 
src_offset,
               mkdir_mode = src_mode & CHMOD_MODE_BITS & ~omitted_permissions;
               if (mkdir (dir, mkdir_mode) != 0)
                 {
-                  error (0, errno, _("cannot make directory %s"),
-                         quote (dir));
-                  return false;
+                  /* If someone else created it between our stat/mkdir,
+                     don't complain.  It's debatable whether we should
+                     also preserve the mode bits in this scenario.  */
+                  if (errno != EEXIST)
+                    {
+                      error (0, errno, _("cannot make directory %s"),
+                             quote (dir));
+                      return false;
+                    }
                 }
               else
                 {
-- 
1.8.0.2