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Message-ID: <20230925112853.6cb7fff3@xps-13>
Date: Mon, 25 Sep 2023 11:28:53 +0200
From: Miquel Raynal <miquel.raynal@...tlin.com>
To: Richard Weinberger <richard@....at>
Cc: ZhaoLong Wang <wangzhaolong1@...wei.com>,
Vignesh Raghavendra <vigneshr@...com>,
linux-mtd <linux-mtd@...ts.infradead.org>,
linux-kernel <linux-kernel@...r.kernel.org>,
chengzhihao1 <chengzhihao1@...wei.com>,
yi zhang <yi.zhang@...wei.com>, yangerkun@...wei.com
Subject: Re: [RFC] mtd: Fix error code loss in mtdchar_read() function.
Hi Richard,
richard@....at wrote on Mon, 25 Sep 2023 11:14:40 +0200 (CEST):
> ----- Ursprüngliche Mail -----
> >> 'total_retlen' is 0, not the error code.
> >
> > Actually after looking at the code, I have no strong opinion
> > regarding whether we should return 0 or an error code in this case.
> >
> > There is this comment right above, and I'm not sure it is still up to
> > date because I believe many drivers just don't provide the data upon
> > ECC error:
> >
> > /* Nand returns -EBADMSG on ECC errors, but it returns
> > * the data. For our userspace tools it is important
> > * to dump areas with ECC errors!
> > * For kernel internal usage it also might return -EUCLEAN
> > * to signal the caller that a bitflip has occurred and has
> > * been corrected by the ECC algorithm.
> > * Userspace software which accesses NAND this way
> > * must be aware of the fact that it deals with NAND
> > */
> >
> >> This problem causes the user-space program to encounter EOF when it has
> >> not finished reading the mtd partion, and this also violates the read
> >> system call standard in POSIX.
>
> This is a special purpose device file and not a regular file.
> Please explain in detail why this violates POSIX and which program breaks.
>
> As pointed out by Miquel, the comment makes it clean that this behavior is
> on purpose. If we return now all of a sudden -EBADMSG for the described
> scenario we might even break existing MTD userspace.
The bugzilla link in the commit log [1] mentions:
* dd would just stop in the middle without showing errors
-> we probably don't care, we expect the userspace to know this is
NAND when dealing with mtd devices directly, dd is not mtd-aware
anyway.
* ubiformat would loop forever
-> that one needs attention I guess :)
[1] https://bugzilla.kernel.org/show_bug.cgi?id=217939
Thanks,
Miquèl
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