[PATCH 0/2] lib/kstrtox: introduce kstrtoull_suffix() helper

[Qu Wenruo <wqu@suse.com>]

Recently David Sterba <dsterba@suse.cz> exposed some weird behavior of
btrfs sysfs interface, which is utilize memparse().

One example is using "echo 25e >
/sys/fs/btrfs/<uuid>/devinfo/scrub_speed_max".

The result value is not 0x25e, because there is no "0x" prefix provided.
Nor (25 << 60), as that would overflow.

All these are the caveats of memparse(), which lacks:

- Overflow check
- Reasonable suffix selection
  I know there may be some niche cases for memory layout, but for most
  callers, they just want a kstrtoull() with reasonable suffix
  selection.
  And I don't think exabytes is a reasonable suffix.

So here we introduce a new helper, "kstrtoull_suffix", which has some
the following two abilities added:

- Allow caller to select the suffix they want to enable
  The default list is "KkMmGgTtPp", no unreasonable "Ee" ones.

- Allow suffix parsing with overflow detection.
  The int part detection is already done by _kstrtoull(), and with the
  extra left shift, do the check again before returning the value.

Unfortunately this new helper is still not a drop-in replacement for
memparse():

- No @retptr support
  It's possible to add, but I'm not sure how many call sites need that
  for extra separators.

- Need to check the failure properly
  Which memparse() callers never seems to check anyway.

Thus the existing memparse() callers need to opt-in.
For now, btrfs usage of memparse() can be easily converted to
kstrtoull_suffix(), in the 2nd patch.

Qu Wenruo (2):
  lib/strtox: introduce kstrtoull_suffix() helper
  btrfs: sysfs: use kstrtoull_suffix() to replace memparse()

 fs/btrfs/sysfs.c        |  20 +++----
 include/linux/kstrtox.h |   7 +++
 lib/kstrtox.c           | 113 ++++++++++++++++++++++++++++++++++++++--
 3 files changed, 123 insertions(+), 17 deletions(-)

-- 
2.43.0