[lxc-devel] [PATCH] utils: reimplement/fix mkdir_p()

[Richard Weinberger]

Am 17.04.2013 22:49, schrieb Serge Hallyn:
> Quoting Richard Weinberger (richard at nod.at):
>> Am 17.04.2013 18:00, schrieb Serge Hallyn:
>>> Quoting Richard Weinberger (richard at nod.at):
>>>> Reimplement mkdir_p() such that it:
>>>>   ...handles relativ paths correctly. (currently it crashes)
>>>>   ...does not rely on dirname().
>>>>   ...is not recursive.
>>>>   ...is shorter. ;-)
>>>
>>> Looks good, thanks.  Yeah I prefer non-recursive.  Three
>>> comments though,
>>>
>>>> Signed-off-by: Richard Weinberger <richard at nod.at>
>>>> ---
>>>>   src/lxc/utils.c | 48 +++++++++++++++++-------------------------------
>>>>   1 file changed, 17 insertions(+), 31 deletions(-)
>>>>
>>>> diff --git a/src/lxc/utils.c b/src/lxc/utils.c
>>>> index e07ca7b..9794553 100644
>>>> --- a/src/lxc/utils.c
>>>> +++ b/src/lxc/utils.c
>>>> @@ -95,39 +95,25 @@ extern int get_u16(unsigned short *val, const char *arg, int base)
>>>>   	return 0;
>>>>   }
>>>>
>>>> -static int is_all_slashes(char *path)
>>>> -{
>>>> -	while (*path && *path == '/')
>>>> -		path++;
>>>> -	if (*path)
>>>> -		return 0;
>>>> -	return 1;
>>>> -}
>>>> -
>>>>   extern int mkdir_p(char *dir, mode_t mode)
>>>>   {
>>>> -	int ret;
>>>> -	char *d;
>>>> -
>>>> -	if (is_all_slashes(dir))
>>>> -		return 0;
>>>> -
>>>> -	d = strdup(dir);
>>>> -	if (!d)
>>>> -		return -1;
>>>> -
>>>> -	ret = mkdir_p(dirname(d), mode);
>>>> -	free(d);
>>>> -	if (ret)
>>>> -		return -1;
>>>> -
>>>> -	if (!access(dir, F_OK))
>>>> -		return 0;
>>>> -
>>>> -	if (mkdir(dir, mode)) {
>>>> -		SYSERROR("failed to create directory '%s'\n", dir);
>>>> -		return -1;
>>>> -	}
>>>> +	char *tmp = dir;
>>>> +	char *orig = dir;
>>>> +	char *makeme;
>>>> +
>>>> +	do {
>>>> +		dir = tmp + strspn(tmp, "/");
>>>> +		tmp = dir + strcspn(dir, "/");
>>>> +		makeme = strndupa(orig, dir - orig);
>>>
>>> strndupa *can* fail and return NULL.
>>
>> How?
>
> I was hoping that smart libc on embedded would return NULL if it sees
> there isn't enough space.  I misread the strndupa manpage to say it
> returns NULL on failure - I see there is no such promise.
>
>> strndupa() uses alloca(), which allocates memory on the stack.
>> *If* it fails we have already overrun the stack and are on a one-way trip
>> to lala land. :-)
>>
>>>
>>>> +		if (*makeme) {
>>>> +			if (!access(makeme, F_OK))
>>>> +				return 0;
>>>
>>> did you mean to continue here?
>>
>> No, if the access() we have to stop.
>               =========
>
> If the access() does what?  access("/var", F_OK) should immediately
> return 0, so you're saying mkdir_p("/var/lib/lxc/c1") should immediately
> fail?  It's entirely possible I'm not thinking right, but...

Please let me dig into mkdir(1) to copy the exact semantics. :-)

Thanks,
//richard