Re: [PATCH U-BOOT v3 25/30] fs: btrfs: Implement btrfs_file_read()

From: Tom Rini <trini@konsulko.com>
To: Qu Wenruo <quwenruo.btrfs@gmx.com>
Cc: "Marek Behún" <marek.behun@nic.cz>,
	u-boot@lists.denx.de,
	"Alberto Sánchez Molero" <alsamolero@gmail.com>,
	"Marek Vasut" <marex@denx.de>,
	"Pierre Bourdon" <delroth@gmail.com>,
	"Simon Glass" <sjg@chromium.org>,
	"Yevgeny Popovych" <yevgenyp@pointgrab.com>,
	linux-btrfs@vger.kernel.org, "Qu Wenruo" <wqu@suse.com>
Subject: Re: [PATCH U-BOOT v3 25/30] fs: btrfs: Implement btrfs_file_read()
Date: Mon, 7 Sep 2020 20:56:46 -0400	[thread overview]
Message-ID: <20200908005646.GG7259@bill-the-cat> (raw)
In-Reply-To: <a88a1a38-8fce-f438-25c9-05d3edd83cf6@gmx.com>

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On Tue, Sep 08, 2020 at 08:26:27AM +0800, Qu Wenruo wrote:
> 
> 
> On 2020/9/8 上午6:35, Tom Rini wrote:
> > On Wed, Jun 24, 2020 at 06:03:11PM +0200, Marek Behún wrote:
> > 
> >> From: Qu Wenruo <wqu@suse.com>
> >>
> >> This version of btrfs_file_read() has the following new features:
> >> - Tries all mirrors
> >> - More handling on unaligned size
> >> - Better compressed extent handling
> >>   The old implementation doesn't handle compressed extent with offset
> >>   properly: we need to read out the whole compressed extent, then
> >>   decompress the whole extent, and only then copy the requested part.
> >>
> >> Signed-off-by: Qu Wenruo <wqu@suse.com>
> >> Reviewed-by: Marek Behún <marek.behun@nic.cz>
> > 
> > Note that this introduces a warning with LLVM-10:
> > fs/btrfs/btrfs.c:246:6: warning: variable 'real_size' is used uninitialized whenever 'if' condition is false [-Wsometimes-uninitialized]
> >         if (!len) {
> >             ^~~~
> > fs/btrfs/btrfs.c:255:12: note: uninitialized use occurs here
> >         if (len > real_size - offset)
> >                   ^~~~~~~~~
> > fs/btrfs/btrfs.c:246:2: note: remove the 'if' if its condition is always true
> >         if (!len) {
> >         ^~~~~~~~~~
> > fs/btrfs/btrfs.c:228:18: note: initialize the variable 'real_size' to silence this warning
> >         loff_t real_size;
> >                         ^
> >                          = 0
> > 1 warning generated.
> > 
> > and I have silenced as suggested.  I'm not 100% happy with that, but
> > leave fixing it here and in upstream btrfs-progs to the btrfs-experts.
> 
> My bad. The warning is correct, and since the code is U-boot specific,
> it doesn't affect kernel (using page) nor btrfs-progs (not really do
> file read with offset).
> 
> The fix is a little complex.
> 
> In fact we need to always call btrfs_size() to grab the real_size, and
> then modify @len using real_size, either using real_size directly, or do
> some basic calculation.

Ah, thanks.  I'll fold in your changes.

> 
> BTW, I didn't see the btrfs rebuild work merged upstream. Is this
> planned or you just grab from some specific branch?

Yes, I'm testing them for -next right now.

-- 
Tom

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