archive mirror
 help / color / mirror / Atom feed
From: "Krzysztof Wilczyński" <>
To: Bjorn Helgaas <>
Cc: Bjorn Helgaas <>,
	Logan Gunthorpe <>,
	Joe Perches <>,
	Oliver O'Halloran <>,
	Michael Ellerman <>,
	Benjamin Herrenschmidt <>,
	Paul Mackerras <>,
	Tyrel Datwyler <>,
	Russell Currey <>,
	Kurt Schwemmer <>,
	Vidya Sagar <>,
	Xiongfeng Wang <>,
Subject: Re: [PATCH v6 5/6] PCI/sysfs: Only show value when driver_override is not NULL
Date: Fri, 4 Jun 2021 00:19:56 +0200	[thread overview]
Message-ID: <20210603221956.GA393910@rocinante.localdomain> (raw)
In-Reply-To: <20210603211741.GA2141918@bjorn-Precision-5520>

Hi Bjorn,

Thank you for the review!

> > Only expose the value of the "driver_override" variable through the
> > corresponding sysfs object when a value is actually set.
> What's the reason for this change?  The above tells me what it *does*,
> but not *why* or whether it affects users.

Good point!  I am going to update the commit message with more details
about why this change in the next version.  Sorry about this!

> Is this to avoid trying to print a NULL pointer as %s?  Do we print
> "(null)" or something in that case now?  I assume sprintf() doesn't
> actually oops.  If we change what appears in sysfs, we should mention
> that here.  And maybe consider whether there's any chance of breaking
> user code that might know what to do with "(null)" but not with an
> empty string.

Yes, sprintf() deals with a NULL pointer and prints "(null)", and
I personally think that this is not very useful, especially in the case
of this particular sysfs object - I would also prefer not to expose the
notion of a NULL-value to the userspace this way, something we ought to
handle properly, see for example how the "resource_alignment" sysfs
object behaves when there is no value set, as per:

  # wc /sys/bus/pci/resource_alignment
     0    0    0 /sys/bus/pci/resource_alignment

> There are six other driver_override_show() methods.  Five don't check
> the ->driver_override pointer at all; one (spi.c) checks like this:
>   len = snprintf(buf, PAGE_SIZE, "%s\n", spi->driver_override ? : "");

For an empty sysfs object, as per the sysfs recommendations, I believe
that having 0 bytes might be more appropriate to indicate lack of any
sensible value.  Using "" (empty string) like in the example above would
still warrant adding a trailing newline character, which would make it
empty (technically), but certainly not 0 bytes.  Having said that, some
drivers opt not to add a particular sysfs object at all should there be
no value for it.

> Do the others need similar fixes?  Most of them still use sprintf()
> also.

I would like to think that we should handle NULL-value in sysfs objects
sensibly everywhere, so the other cases you were able to find could be


  parent reply	other threads:[~2021-06-03 22:20 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-03  0:01 [PATCH v6 0/6] PCI/sysfs: Use sysfs_emit() and sysfs_emit_at() in "show" functions Krzysztof Wilczyński
2021-06-03  0:01 ` [PATCH v6 1/6] " Krzysztof Wilczyński
2021-06-03  0:01 ` [PATCH v6 2/6] PCI/sysfs: Use return value from dsm_label_utf16s_to_utf8s() directly Krzysztof Wilczyński
2021-06-03  0:01 ` [PATCH v6 3/6] PCI/sysfs: Fix trailing newline handling of resource_alignment_param Krzysztof Wilczyński
2021-06-03 23:40   ` Bjorn Helgaas
2021-06-04 13:25     ` Krzysztof Wilczyński
2021-06-03  0:01 ` [PATCH v6 4/6] PCI/sysfs: Add missing trailing newline to devspec_show() Krzysztof Wilczyński
2021-06-03 23:00   ` Bjorn Helgaas
2021-06-03  0:01 ` [PATCH v6 5/6] PCI/sysfs: Only show value when driver_override is not NULL Krzysztof Wilczyński
2021-06-03 21:17   ` Bjorn Helgaas
2021-06-03 21:37     ` Bjorn Helgaas
2021-06-03 22:19     ` Krzysztof Wilczyński [this message]
2021-06-03 23:23   ` Bjorn Helgaas
2021-06-04  0:47     ` Alex Williamson
2021-06-04  1:10       ` Krzysztof Wilczyński
2021-06-03  0:01 ` [PATCH v6 6/6] PCI/sysfs: Fix a buffer overrun problem with dsm_label_utf16s_to_utf8s() Krzysztof Wilczyński
2021-06-04  4:07 ` [PATCH v6 0/6] PCI/sysfs: Use sysfs_emit() and sysfs_emit_at() in "show" functions Bjorn Helgaas
2021-06-04 13:38   ` Krzysztof Wilczyński

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20210603221956.GA393910@rocinante.localdomain \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).