Re: [PATCH 07/11] fuse: restructure fuse_readpage()

From: Maxim Patlasov
Date: Mon Jan 20 2014 - 06:46:44 EST

On 01/06/2014 08:43 PM, Miklos Szeredi wrote:
On Fri, Dec 20, 2013 at 06:54:40PM +0400, Maxim Patlasov wrote:
Hi Miklos,

Sorry for delay, see please inline comments below.

On 11/12/2013 09:17 PM, Miklos Szeredi wrote:
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

Signed-off-by: Maxim Patlasov <MPatlasov@xxxxxxxxxxxxx>
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'.
fuse_readpage() passes 'req' to fuse_short_read(). And the latter
uses req->pages[] to nullify a part of request.
I don't get it. __fuse_readpage() itself call's fuse_short_read(), not callers
of __fuse_readpage(). Or do they?

fuse_readpage() is a caller of __fuse_readpage() and it looks (after applying the patch) like this:

> static int fuse_readpage(struct file *file, struct page *page)
> {
> ...
> num_read = __fuse_readpage(file, page, count, &err, &req, &attr_ver);
> if (!err) {
> /*
> * Short read means EOF. If file size is larger, truncate it
> */
> if (num_read < count)
> fuse_short_read(req, inode, attr_ver);
> SetPageUptodate(page);
> }


And fuse_get_attr_version() can be moved to the
one caller that needs it.
Yes, it's doable. But this would make attr_version mechanism less
efficient (under some loads): suppose the file on server was
truncated externally, then fuse_readpage() acquires
fc->attr_version, then some innocent write bumps fc->attr_version
while we're waiting for fuse writeback, then fuse_read_update_size()
would noop. In the other words, it's beneficial to keep the time
interval between acquiring fc->attr_version and subsequent
comparison as short as possible.
Okay, lets try to keep this the way it is. I don't like it very much, but I
fear changing user visible behavior.


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