linux-kernel - Re: [PATCH v1 05/23] netfs: add inode parameter to netfs_alloc_read

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Message-ID: <YdRS4AnHbWpHwl/8@B-P7TQMD6M-0146.local>
Date:   Tue, 4 Jan 2022 22:00:00 +0800
From:   Gao Xiang <hsiangkao@...ux.alibaba.com>
To:     Jeffle Xu <jefflexu@...ux.alibaba.com>
Cc:     dhowells@...hat.com, linux-cachefs@...hat.com, xiang@...nel.org,
        chao@...nel.org, linux-erofs@...ts.ozlabs.org,
        linux-fsdevel@...r.kernel.org, joseph.qi@...ux.alibaba.com,
        bo.liu@...ux.alibaba.com, tao.peng@...ux.alibaba.com,
        gerry@...ux.alibaba.com, eguan@...ux.alibaba.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 05/23] netfs: add inode parameter to
 netfs_alloc_read_request()

On Mon, Dec 27, 2021 at 08:54:26PM +0800, Jeffle Xu wrote:
> When working as the local cache, the @file parameter of
> netfs_alloc_read_request() represents the backed file inside netfs. It
> is for two use: 1) we can derive the corresponding inode from file,
> 2) works as the argument for ops->init_rreq().
> 
> In the new introduced demand-read mode, netfs_readpage() will be called
> by the upper fs to read from backing files. However in this new mode,
> the backed file may not be opened, and thus the @file argument is NULL
> in this case.
> 
> For netfs_readpage(), @file parameter represents the backed file inside
> netfs, while @folio parameter represents one page cache inside the
> address space of this backed file. We can still derive the inode from
> the @folio parameter, even when @file parameter is NULL.
> 
> Thus refactor netfs_alloc_read_request() somewhat for this change.
> 
> Signed-off-by: Jeffle Xu <jefflexu@...ux.alibaba.com>

I'm not sure how other folks think.

Yet in principle, personally I think it's reasonable that
something like read_cache_page_gfp() could be used directly
with fscache backend as well.

So for such internal read requests, @file argument is
actually optional as a common practice.

Apart from the commit message itself (which I think it could
be simplified a bit), generally it looks good to me.

Thanks,
Gao Xiang


> ---
>  fs/netfs/read_helper.c | 12 +++++++-----
>  1 file changed, 7 insertions(+), 5 deletions(-)
> 
> diff --git a/fs/netfs/read_helper.c b/fs/netfs/read_helper.c
> index 8c58cff420ba..ca84918b6b5d 100644
> --- a/fs/netfs/read_helper.c
> +++ b/fs/netfs/read_helper.c
> @@ -39,7 +39,7 @@ static void netfs_put_subrequest(struct netfs_read_subrequest *subreq,
>  
>  static struct netfs_read_request *netfs_alloc_read_request(
>  	const struct netfs_read_request_ops *ops, void *netfs_priv,
> -	struct file *file)
> +	struct inode *inode, struct file *file)
>  {
>  	static atomic_t debug_ids;
>  	struct netfs_read_request *rreq;
> @@ -48,7 +48,7 @@ static struct netfs_read_request *netfs_alloc_read_request(
>  	if (rreq) {
>  		rreq->netfs_ops	= ops;
>  		rreq->netfs_priv = netfs_priv;
> -		rreq->inode	= file_inode(file);
> +		rreq->inode	= inode;
>  		rreq->i_size	= i_size_read(rreq->inode);
>  		rreq->debug_id	= atomic_inc_return(&debug_ids);
>  		INIT_LIST_HEAD(&rreq->subrequests);
> @@ -870,6 +870,7 @@ void netfs_readahead(struct readahead_control *ractl,
>  		     void *netfs_priv)
>  {
>  	struct netfs_read_request *rreq;
> +	struct inode *inode = file_inode(ractl->file);
>  	unsigned int debug_index = 0;
>  	int ret;
>  
> @@ -878,7 +879,7 @@ void netfs_readahead(struct readahead_control *ractl,
>  	if (readahead_count(ractl) == 0)
>  		goto cleanup;
>  
> -	rreq = netfs_alloc_read_request(ops, netfs_priv, ractl->file);
> +	rreq = netfs_alloc_read_request(ops, netfs_priv, inode, ractl->file);
>  	if (!rreq)
>  		goto cleanup;
>  	rreq->mapping	= ractl->mapping;
> @@ -948,12 +949,13 @@ int netfs_readpage(struct file *file,
>  		   void *netfs_priv)
>  {
>  	struct netfs_read_request *rreq;
> +	struct inode *inode = folio_file_mapping(folio)->host;
>  	unsigned int debug_index = 0;
>  	int ret;
>  
>  	_enter("%lx", folio_index(folio));
>  
> -	rreq = netfs_alloc_read_request(ops, netfs_priv, file);
> +	rreq = netfs_alloc_read_request(ops, netfs_priv, inode, file);
>  	if (!rreq) {
>  		if (netfs_priv)
>  			ops->cleanup(folio_file_mapping(folio), netfs_priv);
> @@ -1122,7 +1124,7 @@ int netfs_write_begin(struct file *file, struct address_space *mapping,
>  	}
>  
>  	ret = -ENOMEM;
> -	rreq = netfs_alloc_read_request(ops, netfs_priv, file);
> +	rreq = netfs_alloc_read_request(ops, netfs_priv, inode, file);
>  	if (!rreq)
>  		goto error;
>  	rreq->mapping		= folio_file_mapping(folio);
> -- 
> 2.27.0