linux-kernel - Re: [PATCH 07/11] fuse: restructure fuse

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Message-ID: <20131112171707.GB10813@tucsk.piliscsaba.szeredi.hu>
Date:	Tue, 12 Nov 2013 18:17:07 +0100
From:	Miklos Szeredi <miklos@...redi.hu>
To:	Maxim Patlasov <MPatlasov@...allels.com>
Cc:	dev@...allels.com, xemul@...allels.com,
	fuse-devel@...ts.sourceforge.net, bfoster@...hat.com,
	linux-kernel@...r.kernel.org, jbottomley@...allels.com,
	linux-fsdevel@...r.kernel.org, akpm@...ux-foundation.org,
	fengguang.wu@...el.com, devel@...nvz.org
Subject: Re: [PATCH 07/11] fuse: restructure fuse_readpage()

On Thu, Oct 10, 2013 at 05:11:25PM +0400, Maxim Patlasov wrote:
> Move the code filling and sending read request to a separate function. Future
> patches will use it for .write_begin -- partial modification of a page
> requires reading the page from the storage very similarly to what fuse_readpage
> does.
> 
> Signed-off-by: Maxim Patlasov <MPatlasov@...allels.com>
> ---
>  fs/fuse/file.c |   55 +++++++++++++++++++++++++++++++++++++------------------
>  1 file changed, 37 insertions(+), 18 deletions(-)
> 
> diff --git a/fs/fuse/file.c b/fs/fuse/file.c
> index b4d4189..77eb849 100644
> --- a/fs/fuse/file.c
> +++ b/fs/fuse/file.c
> @@ -700,21 +700,14 @@ static void fuse_short_read(struct fuse_req *req, struct inode *inode,
>  	}
>  }
>  
> -static int fuse_readpage(struct file *file, struct page *page)
> +static int __fuse_readpage(struct file *file, struct page *page, size_t count,
> +			   int *err, struct fuse_req **req_pp, u64 *attr_ver_p)

Signature of this helper looks really ugly.  A quick look tells me that neither
caller actually needs 'req'.  And fuse_get_attr_version() can be moved to the
one caller that needs it.  And negative err can be returned.  And then all those
ugly pointer args are gone and the whole thing is much simpler.

Thanks,
Miklos



>  {
>  	struct fuse_io_priv io = { .async = 0, .file = file };
>  	struct inode *inode = page->mapping->host;
>  	struct fuse_conn *fc = get_fuse_conn(inode);
>  	struct fuse_req *req;
>  	size_t num_read;
> -	loff_t pos = page_offset(page);
> -	size_t count = PAGE_CACHE_SIZE;
> -	u64 attr_ver;
> -	int err;
> -
> -	err = -EIO;
> -	if (is_bad_inode(inode))
> -		goto out;
>  
>  	/*
>  	 * Page writeback can extend beyond the lifetime of the
> @@ -724,20 +717,45 @@ static int fuse_readpage(struct file *file, struct page *page)
>  	fuse_wait_on_page_writeback(inode, page->index);
>  
>  	req = fuse_get_req(fc, 1);
> -	err = PTR_ERR(req);
> +	*err = PTR_ERR(req);
>  	if (IS_ERR(req))
> -		goto out;
> +		return 0;
>  
> -	attr_ver = fuse_get_attr_version(fc);
> +	if (attr_ver_p)
> +		*attr_ver_p = fuse_get_attr_version(fc);
>  
>  	req->out.page_zeroing = 1;
>  	req->out.argpages = 1;
>  	req->num_pages = 1;
>  	req->pages[0] = page;
>  	req->page_descs[0].length = count;
> -	num_read = fuse_send_read(req, &io, pos, count, NULL);
> -	err = req->out.h.error;
>  
> +	num_read = fuse_send_read(req, &io, page_offset(page), count, NULL);
> +	*err = req->out.h.error;
> +
> +	if (*err)
> +		fuse_put_request(fc, req);
> +	else
> +		*req_pp = req;
> +
> +	return num_read;
> +}
> +
> +static int fuse_readpage(struct file *file, struct page *page)
> +{
> +	struct inode *inode = page->mapping->host;
> +	struct fuse_conn *fc = get_fuse_conn(inode);
> +	struct fuse_req *req = NULL;
> +	size_t num_read;
> +	size_t count = PAGE_CACHE_SIZE;
> +	u64 attr_ver = 0;
> +	int err;
> +
> +	err = -EIO;
> +	if (is_bad_inode(inode))
> +		goto out;
> +
> +	num_read = __fuse_readpage(file, page, count, &err, &req, &attr_ver);
>  	if (!err) {
>  		/*
>  		 * Short read means EOF.  If file size is larger, truncate it
> @@ -747,10 +765,11 @@ static int fuse_readpage(struct file *file, struct page *page)
>  
>  		SetPageUptodate(page);
>  	}
> -
> -	fuse_put_request(fc, req);
> -	fuse_invalidate_attr(inode); /* atime changed */
> - out:
> +	if (req) {
> +		fuse_put_request(fc, req);
> +		fuse_invalidate_attr(inode); /* atime changed */
> +	}
> +out:
>  	unlock_page(page);
>  	return err;
>  }
> 
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