[v4 PATCH 0/1] x86/resctrl: Add "*" shorthand to set io_alloc CBM for all domains

[Aaron Tomlin <atomlin@atomlin.com>]

Hi Babu, Tony, Reinette,

This patch introduces a wildcard domain ID selector "*" for the
io_alloc_cbm interface. It allows a user to update the Capacity Bitmask
(CBM) across all cache domains in a single operation.

Currently, configuring io_alloc_cbm requires an explicit ID for each
domain, which is cumbersome on systems with high core counts and numerous
cache clusters. Supporting a wildcard selector simplifies automation and
management tasks.

For example, a user can now write "*=0" to the io_alloc_cbm file to program
every domain to the hardware-defined minimum CBM. Note that the value
provided must still adhere to the constraints defined in the resource's
min_cbm_bits.

Please let me know your thoughts.


Changes since v3 [1]:
 - Updated the wildcard documentation text to be clearer and less
   prescriptive (Reinette Chatre)

 - Reverted the while loop refactoring in resctrl_io_alloc_parse_line() to
   restore the standard parsing pattern and prevent invalid domain ID
   regressions (Reinette Chatre)

 - Added explicit validation to ensure the wildcard selector is followed by
   a value assignment (Reinette Chatre)

 - Restored memcpy() usage for configuration copying to minimise unrelated
   diff noise

Changes since v2 [2]:
 - Dropped return -EINVAL for a missing seq_show implementation
   (Reinette Chatre)
 - Dropped helpers to check io_alloc support and enabled state
   (Reinette Chatre)
 - Removed additional complexity (Babu Moger)
 - Introduced the "*" wildcard for io_alloc_cbm to allow updating all
   cache domains (Reinette Chatre)
 - Replaced goto-based line parsing with a while loop to support
   multi-domain and wildcard iterations
 - Replaced memcpy() with direct structure assignment

Changes since v1 [3]:
 - Updated each helper for consistency (Babu Moger)
 - Refactored the loop logic in function resctrl_io_alloc_parse_line()
   to improve readability
 - Added inline keyword to each helper
 - Added inline keyword to function parse_domain_cbm()

[1]: https://lore.kernel.org/lkml/20251231023549.2390630-1-atomlin@atomlin.com/
[2]: https://lore.kernel.org/lkml/20251215230257.1798865-1-atomlin@atomlin.com/
[3]: https://lore.kernel.org/lkml/20251126171653.1004321-1-atomlin@atomlin.com/

Aaron Tomlin (1):
  x86/resctrl: Add "*" shorthand to set io_alloc CBM for all domains

 Documentation/filesystems/resctrl.rst |  8 ++++++++
 fs/resctrl/ctrlmondata.c              | 20 +++++++++++++++++---
 2 files changed, 25 insertions(+), 3 deletions(-)

-- 
2.51.0