[sheepdog] [PATCH] sheep: lock against concurrent access to the store directory

[Liu Yuan]

On 05/17/2012 11:40 PM, Christoph Hellwig wrote:

> This patch uses lockf on a specially create lock file in the base directory
> to detect early on if another sheep is using this directory and abort with
> a useful error message.
> 
> Signed-off-by: Christoph Hellwig <hch at lst.de>
> 
> diff --git a/sheep/store.c b/sheep/store.c
> index 5d433f3..e93daef 100644
> --- a/sheep/store.c
> +++ b/sheep/store.c
> @@ -672,11 +672,40 @@ again:
>  	return 0;
>  }
>  
> +#define LOCK_PATH "/lock"
> +
>  int init_base_path(const char *d)
>  {
>  	int new = 0;
> +	int ret;
> +	int fd;
> +	char *lock_path;
> +
> +	ret = init_path(d, &new);
> +	if (ret)
> +		return ret;
> +
> +	lock_path = zalloc(strlen(d) + strlen(LOCK_PATH) + 1);
> +	sprintf(lock_path, "%s" LOCK_PATH, d);
> +
> +	fd = open(lock_path, O_WRONLY|O_CREAT, def_fmode);
> +	if (fd < 0) {
> +		eprintf("failed to open lock file %s (%s)\n",
> +			lock_path, strerror(errno));
> +		return -1;
> +	}
> +		
> +	if (lockf(fd, F_TLOCK, 1) < 0) {
> +		if (errno == EACCES || errno == EAGAIN) {
> +			eprintf("another sheep daemon is using %s\n", d);
> +		} else {
> +			eprintf("unable to get base dir lock (%s)\n",
> +				strerror(errno));
> +		}
> +		return -1;
> +	}
>  
> -	return init_path(d, &new);
> +	return 0;
>  }
>  


Should free(lock_path), or use stack to allocate the space.

Thanks,
Yuan

>  #define OBJ_PATH "/obj/"