Re: [PATCH 4/5] safe_create_leading_directories(): fix a mkdir/rmdir race

> It could be that some other process is trying to clean up empty
> directories at the same time that safe_create_leading_directories() is
> attempting to create them.  In this case, it could happen that
> directory "a/b" was present at the end of one iteration of the loop
> (either it was already present or we just created it ourselves), but
> by the time we try to create directory "a/b/c", directory "a/b" has
> been deleted.  In fact, directory "a" might also have been deleted.
> 
> So, if a call to mkdir() fails with ENOENT, then try checking/making
> all directories again from the beginning.  Attempt up to three times
> before giving up.
> 
> Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
> ---
>  sha1_file.c | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/sha1_file.c b/sha1_file.c
> index dcfd35a..abcb56b 100644
> --- a/sha1_file.c
> +++ b/sha1_file.c
> @@ -108,6 +108,7 @@ int mkdir_in_gitdir(const char *path)
>  int safe_create_leading_directories(char *path)
>  {
>  	char *next_component = path + offset_1st_component(path);
> +	int attempts = 3;
>  	int retval = 0;
>  
>  	while (!retval && next_component) {
> @@ -132,6 +133,16 @@ int safe_create_leading_directories(char *path)
>  			if (errno == EEXIST &&
>  			    !stat(path, &st) && S_ISDIR(st.st_mode)) {
>  				; /* somebody created it since we checked */
> +			} else if (errno == ENOENT && --attempts) {
> +				/*
> +				 * Either mkdir() failed bacause

> +				 * somebody just pruned the containing
> +				 * directory, or stat() failed because
> +				 * the file that was in our way was
> +				 * just removed.  Either way, try
> +				 * again from the beginning:
> +				 */
> +				next_component = path + offset_1st_component(path);
>  			} else {
>  				retval = -1;
>  			}
>