Re: [PATCH v7 0/6] PCI/sysfs: Use sysfs_emit() and sysfs_emit_at() in "show" functions

[Bjorn Helgaas <helgaas@kernel.org>]

On Fri, Jun 04, 2021 at 01:32:24PM +0000, Krzysztof Wilczyński wrote:
> Hello,
> 
> This series aims to bring support for the sysfs_emit() and
> sysfs_emit_at() functions to the existing PCI-related sysfs objects.
> These new functions were introduced to make it less ambiguous which
> function is preferred when writing to the output buffer in a device
> attribute's "show" callback [1].
> 
> Thus, the existing PCI sysfs objects "show" functions will be converted
> from the using the sprintf(), snprintf() and scnprintf() functions to
> sysfs_emit() and sysfs_emit_at() accordingly, as the latter is aware of
> the PAGE_SIZE buffer limit that the sysfs object has and correctly
> returns the number of bytes written into the buffer.
> 
> This series will also address inconsistency related to the presence (or
> lack of thereof) of a trailing newline in the show() functions adding it
> where it's currently missing.  This will allow for utilities such as the
> "cat" command to display the result of the read from a particular sysfs
> object correctly in a shell.
> 
> While working on this series a problem with newline handling related to
> how the value of the "resource_alignment" sysfs object was parsed and
> then persisted has been found and corrected.  Also, while at it,
> a change enabling support for the value of "resource_alignment"
> previously set using either a command-line argument or through the sysfs
> object to be cleared at run-time was also included, and thus aligning
> this particular sysfs object with the behaviour of other such objects
> that allow for the value to be dynamically updated and cleared as
> required.
> 
> Additionally, a fix to a potential buffer overrun that has been found in
> the dsm_label_utf16s_to_utf8s() function that is responsible for the
> character conversion from UTF16 to UTF8 of the buffer that holds the
> device label obtained through the ACPI _DSM mechanism is included as
> part of this series.
> 
> Finally, a minor fix is also included in this series that has been added
> to ensure that the value of the "driver_override" variable is only
> exposed through the corresponding sysfs object when a value is set or
> otherwise if the value has not been set, the object would return
> a string representation of the NULL value.  This will also align this
> particular sysfs object's behaviour with others, where when there is no
> value then nothing is returned.
> 
> [1] Documentation/filesystems/sysfs.rst
> 
> This series is related to:
>   commit ad025f8 ("PCI/sysfs: Use sysfs_emit() and sysfs_emit_at() in "show" functions")
> 
> Signed-off-by: Krzysztof Wilczyński <kw@linux.com>

I updated my pci/sysfs branch to include the kfree fix in "PCI/sysfs:
Fix trailing newline handling of resource_alignment_param".

As I mentioned in the v6, I reordered things a bit and dropped
"PCI/sysfs: Only show value when driver_override is not NULL" to avoid
breaking userspace.

It's conceivable that these could break userspace, too, but I think
it's unlikely:

  PCI/sysfs: Fix trailing newline handling of resource_alignment_param
  PCI/sysfs: Add missing trailing newline to devspec_show()

/sys/bus/pci/resource_alignment is a one-off thing and the previous
behavior was clearly incorrect.

There are six varieties of /sys/.../devspec attributes, and all but
the PCI one already include a trailing newline, so anything that
looked at more than the PCI one would have had to deal with the
inconsistency already.

> ---
> Changes in v2:
>   None.
> 
> Changes in v3:
>   Added Logan Gunthorpe's "Reviewed-by".
> 
> Changes in v4:
>   Separated and squashed all the trivial sysfs_emit()/sysfs_emit_at()
>   changes into a single patch as per Bjorn Helgaas' request.
>   Carried Logan Gunthorpe's "Reviewed-by" over.
> 
> Changes in v5:
>   Added check to the resource_alignment_show() function to ensure that
>   there is an extra space left in the buffer for the newline character,
>   assuming that it might be provided.
> 
> Changes in v6:
>   Added a cover letter as per Bjorn Helgaas' request.
>   New patch addressing a potential buffer overrun in the
>   dsm_label_utf16s_to_utf8s() function has been added.
> 
> Changes in v7:
>   Use correct variable name in the resource_alignment_store() function
>   when freeing allocation made using kstrndup() if the value sent from
>   the userspace is an empty string intended to clear the currently set
>   resource alignment.
> 
> Krzysztof Wilczyński (6):
>   PCI/sysfs: Use sysfs_emit() and sysfs_emit_at() in "show" functions
>   PCI/sysfs: Use return value from dsm_label_utf16s_to_utf8s() directly
>   PCI/sysfs: Fix trailing newline handling of resource_alignment_param
>   PCI/sysfs: Add missing trailing newline to devspec_show()
>   PCI/sysfs: Only show value when driver_override is not NULL
>   PCI/sysfs: Fix a buffer overrun problem with
>     dsm_label_utf16s_to_utf8s()
> 
>  drivers/pci/hotplug/pci_hotplug_core.c |  8 +++---
>  drivers/pci/hotplug/rpadlpar_sysfs.c   |  4 +--
>  drivers/pci/hotplug/shpchp_sysfs.c     | 38 ++++++++++++++------------
>  drivers/pci/iov.c                      | 12 ++++----
>  drivers/pci/msi.c                      |  8 +++---
>  drivers/pci/p2pdma.c                   |  7 ++---
>  drivers/pci/pci-label.c                | 22 ++++++++-------
>  drivers/pci/pci-sysfs.c                |  7 +++--
>  drivers/pci/pci.c                      | 34 +++++++++++++----------
>  drivers/pci/pcie/aer.c                 | 20 ++++++++------
>  drivers/pci/pcie/aspm.c                |  4 +--
>  drivers/pci/slot.c                     | 18 ++++++------
>  drivers/pci/switch/switchtec.c         | 18 ++++++------
>  13 files changed, 107 insertions(+), 93 deletions(-)
> 
> -- 
> 2.31.1
>