PCI/sysfs: Use kstrtobool() to parse the ROM attribute input

PCI/sysfs: Use kstrtobool() to parse the ROM attribute input

pci_write_rom() controls access to the ROM content through the
corresponding sysfs attribute, and treats the input as a request to
disable only when it matches the string "0\n" exactly:

  if ((off ==  0) && (*buf == '0') && (count == 2))

The count == 2 condition encodes the trailing newline that echo(1) appends.
This was found when userspace wrote "0" without a trailing newline aiming
to disable access, which failed to match the condition above and enabled
access instead.  For example:

  $ echo 0 > rom       # "0\n", count 2, access disabled
  $ echo -n 0 > rom    # "0", count 1, access enabled
  $ echo > rom         # "", count 1, access enabled (likely not desirable)

Parse the input with kstrtobool(), which handles common boolean inputs such
as "0", "1", "n", "y" or "off", "on", with or without a trailing newline,
so both of the above disable access, and update the now stale comment.

As a side effect, input that does not parse as a boolean is rejected with
-EINVAL rather than enabling access.  The documented "0" and "1" continue
to work as before, and rejecting malformed input brings the attribute in
line with how sysfs attributes typically handle it.

Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Link: https://patch.msgid.link/20260612182448.552406-1-kwilczynski@kernel.org