linux-kernel - Re: [PATCH v2] crypto: hisilicon - allow smaller reads in debugfs

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Message-ID: <20200605091324.GR30374@kadam>
Date:   Fri, 5 Jun 2020 12:13:24 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Shukun Tan <tanshukun1@...wei.com>
Cc:     b6da310b-e633-9f74-f7af-7791d803aaf5@...wei.com,
        Zhou Wang <wangzhou1@...ilicon.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        "David S. Miller" <davem@...emloft.net>,
        linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel-janitors@...r.kernel.org
Subject: Re: [PATCH v2] crypto: hisilicon - allow smaller reads in debugfs

On Fri, Jun 05, 2020 at 09:19:53AM +0800, Shukun Tan wrote:
> Hi Dan,
> 
> On 2020/6/2 21:54, Dan Carpenter wrote:
> > Originally this code rejected any read less than 256 bytes.  There
> > is no need for this artificial limit.  We should just use the normal
> > helper functions to read a string from the kernel.
> > 
> > Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>
> > ---
> > v2: Use simple_read_from_buffer().  The v1 was slightly half arsed
> > because I left the original check for:
> > 
> > 	if (*pos)
> > 		return 0;
> > 
> > So it could result in partial reads.  The new code means that if you
> > want to read the buffer one byte at a time, that's fine or if you want
> > to read it in one 256 byte chunk that's also fine.  Plus it deletes 21
> > lines of code and is a lot cleaner.
> > 
> 
> In fact, In our original design, we do not hope the user do the partial reads.
> Thank you for your work, but I still insist on adding this limit.

This not how POSIX filesystems work...  :(  Last time you said that this
literally breaks cat.

This doesn't break anything if the user chooses not to read a single
byte at a time.  That's obviously a crazy way to read a file.  It just
allows them to if they want.  Or if they want to read 256 bytes at a
time then that also works.  My patch makes *everything* work.

regards,
dan carpenter