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Message-ID: <20180110140149.GA5174@linux-zmni.DHCP> Date: Wed, 10 Jan 2018 22:01:49 +0800 From: Sean Fu <fxinrong@...il.com> To: Al Viro <viro@...IV.linux.org.uk> Cc: tytso@....edu, adilger.kernel@...ger.ca, linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH] ext4: Remove repeated test in ext4_file_read_iter. On Wed, Jan 03, 2018 at 02:08:05AM +0000, Al Viro wrote: > On Wed, Dec 27, 2017 at 04:19:58PM +0800, Sean Fu wrote: > > generic_file_read_iter has done the count test. > > So ext4_file_read_iter don't need to test the count repeatedly. > > Huh? You do realize that generic_file_read_iter() is not the > only variant possible there, right? > Yes, I know that generic_file_read_iter() is not the only variant possible. The other possible dax_iomap_rw() with zero count would return zero. > static ssize_t ext4_dax_read_iter(struct kiocb *iocb, struct iov_iter *to) > { > struct inode *inode = file_inode(iocb->ki_filp); > ssize_t ret; > > if (!inode_trylock_shared(inode)) { > if (iocb->ki_flags & IOCB_NOWAIT) > return -EAGAIN; > inode_lock_shared(inode); > } > > ... and now IOCB_NOWAIT read with zero count can fail with -EAGAIN. > Correct, IOCB_NOWAIT read with zero count can return -EAGAIN, But I think that it is reasonable. while it got lock, zero would be returned in this case.
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