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

[Maxim Patlasov]

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
> > > > does.
> > > >
> > > > 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);
>    }

Thanks,
Maxim

> > > 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.
>
> Thanks,
> Miklos

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/