Re: [PATCH v5 33/40] netfs, cachefiles: Pass upper bound length to allow expansion

[Gao Xiang <hsiangkao@xxxxxxxxxxxxxxxxx>]

On 2024/1/3 01:11, David Howells wrote:
> Gao Xiang <hsiangkao@xxxxxxxxxxxxxxxxx> wrote:
>
> > >    	down = start - round_down(start, PAGE_SIZE);
> > >    	*_start = start - down;
> > >    	*_len = round_up(down + len, PAGE_SIZE);
> > > +	if (down < start || *_len > upper_len)
> > > +		return -ENOBUFS;
> >
> > Sorry for bothering. We just found some strange when testing
> > today-next EROFS over fscache.
> >
> > I'm not sure the meaning of
> >      if (down < start
> >
> > For example, if start is page-aligned, down == 0.
> >
> > so as long as start > 0 and page-aligned, it will return
> > -ENOBUFS.  Does it an intended behavior?
>
> Yeah, I think that's wrong.
>
> Does the attached help?

(+cc more people for testing)

Will test and feedback later.

Thanks,
Gao Xiang

> David
> ---
>
> diff --git a/fs/cachefiles/io.c b/fs/cachefiles/io.c
> index bffffedce4a9..7529b40bc95a 100644
> --- a/fs/cachefiles/io.c
> +++ b/fs/cachefiles/io.c
> @@ -522,16 +522,22 @@ int __cachefiles_prepare_write(struct cachefiles_object *object,
>   			       bool no_space_allocated_yet)
>   {
>   	struct cachefiles_cache *cache = object->volume->cache;
> -	loff_t start = *_start, pos;
> -	size_t len = *_len, down;
> +	unsigned long long start = *_start, pos;
> +	size_t len = *_len;
>   	int ret;
>   
>   	/* Round to DIO size */
> -	down = start - round_down(start, PAGE_SIZE);
> -	*_start = start - down;
> -	*_len = round_up(down + len, PAGE_SIZE);
> -	if (down < start || *_len > upper_len)
> +	start = round_down(*_start, PAGE_SIZE);
> +	if (start != *_start) {
> +		kleave(" = -ENOBUFS [down]");
> +		return -ENOBUFS;
> +	}
> +	if (*_len > upper_len) {
> +		kleave(" = -ENOBUFS [up]");
>   		return -ENOBUFS;
> +	}
> +
> +	*_len = round_up(len, PAGE_SIZE);
>   
>   	/* We need to work out whether there's sufficient disk space to perform
>   	 * the write - but we can skip that check if we have space already
> @@ -542,7 +548,7 @@ int __cachefiles_prepare_write(struct cachefiles_object *object,
>   
>   	pos = cachefiles_inject_read_error();
>   	if (pos == 0)
> -		pos = vfs_llseek(file, *_start, SEEK_DATA);
> +		pos = vfs_llseek(file, start, SEEK_DATA);
>   	if (pos < 0 && pos >= (loff_t)-MAX_ERRNO) {
>   		if (pos == -ENXIO)
>   			goto check_space; /* Unallocated tail */
> @@ -550,7 +556,7 @@ int __cachefiles_prepare_write(struct cachefiles_object *object,
>   					  cachefiles_trace_seek_error);
>   		return pos;
>   	}
> -	if ((u64)pos >= (u64)*_start + *_len)
> +	if (pos >= start + *_len)
>   		goto check_space; /* Unallocated region */
>   
>   	/* We have a block that's at least partially filled - if we're low on
> @@ -563,13 +569,13 @@ int __cachefiles_prepare_write(struct cachefiles_object *object,
>   
>   	pos = cachefiles_inject_read_error();
>   	if (pos == 0)
> -		pos = vfs_llseek(file, *_start, SEEK_HOLE);
> +		pos = vfs_llseek(file, start, SEEK_HOLE);
>   	if (pos < 0 && pos >= (loff_t)-MAX_ERRNO) {
>   		trace_cachefiles_io_error(object, file_inode(file), pos,
>   					  cachefiles_trace_seek_error);
>   		return pos;
>   	}
> -	if ((u64)pos >= (u64)*_start + *_len)
> +	if (pos >= start + *_len)
>   		return 0; /* Fully allocated */
>   
>   	/* Partially allocated, but insufficient space: cull. */
> @@ -577,7 +583,7 @@ int __cachefiles_prepare_write(struct cachefiles_object *object,
>   	ret = cachefiles_inject_remove_error();
>   	if (ret == 0)
>   		ret = vfs_fallocate(file, FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE,
> -				    *_start, *_len);
> +				    start, *_len);
>   	if (ret < 0) {
>   		trace_cachefiles_io_error(object, file_inode(file), ret,
>   					  cachefiles_trace_fallocate_error);