Steven Walter <[email protected]> writes:
> If two processes are racing to create the same directory tree, they will
> both see that the directory doesn't exist, both try to mkdir(), and one
> of them will fail. This is okay, as we only care that the directory
> gets created. So, we add a check for EEXIST from mkdir, and continue if
> the directory now exists.
>
> Signed-off-by: Steven Walter <[email protected]>
> ---
> sha1_file.c | 9 +++++++++
> 1 file changed, 9 insertions(+)
>
> diff --git a/sha1_file.c b/sha1_file.c
> index 40b2329..5668ecc 100644
> --- a/sha1_file.c
> +++ b/sha1_file.c
> @@ -123,6 +123,15 @@ int safe_create_leading_directories(char *path)
> }
> }
> else if (mkdir(path, 0777)) {
> + if (errno == EEXIST) {
> + /*
> + * We could be racing with another process to
> + * create the directory. As long as the
> + * directory gets created, we don't care.
> + */
> + if (stat(path, &st) && S_ISDIR(st.st_mode))
> + continue;
You probably meant !stat() here, "we can successfully stat() and it
turns out that we already have a directory there, so let's not do
the error thing".
Don't you need to restore (*pos = '/') before doing anything else,
like "continue", by the way? We were given "a/b/c", and in order to
make sure "a" exists, we made it to "a\0b/c", did a stat() and found
it was missing, did a mkdir() and now we got EEXIST. pos points at
that NUL, so I would imagine that in order to continue you need to
* restore the string to be "a/b/c"; and
* make pos to point at "b" in the string.
Perhaps something like this instead?
sha1_file.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)
diff --git a/sha1_file.c b/sha1_file.c
index 9152974..964c4d4 100644
--- a/sha1_file.c
+++ b/sha1_file.c
@@ -122,8 +122,13 @@ int safe_create_leading_directories(char *path)
}
}
else if (mkdir(path, 0777)) {
- *pos = '/';
- return -1;
+ if (errno == EEXIST &&
+ !stat(path, &st) && S_ISDIR(st.st_mode)) {
+ ; /* somebody created it since we checked */
+ } else {
+ *pos = '/';
+ return -1;
+ }
}
else if (adjust_shared_perm(path)) {
*pos = '/';
--
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