Development notes

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Collection of various notes about development practices, how-to's or checklists.

Contents

Misc notes

Adding a new ioctl, extending an existing one

  • add code to strace so the ioctl calls are parsed into a human readable form. Most of the ioctls are already implemented and can be used a reference.

Tracepoints

The tracepoint message format should be compact and consistent, so please stick to the following format:

  • key=value no spaces around =
  • separated by spaces, not commas
  • named values: print value and string, like "%llu(%s)", no space between, string in parens
  • avoid abbreviating key values too much, (eg. use 'size' not 'sz')
  • hexadecimal values are always preceded by 0x (use "0x%llx)

Example:

event: btrfs__chunk

string:

  "root=%llu(%s) offset=%llu size=%llu num_stripes=%d sub_stripes=%d type=%s"

Kernel config options

Testing

Compile-time config options for kernel that can help debugging, testing. They usually take a hit on performance or resources (memory) so they should be selected wisely. The options in bold should be safe to use by default for debugging builds.

Please refer to the option documentation for further details.

  • devices for testing
    • CONFIG_BLK_DEV_LOOP - enable loop device
    • for fstests: DM_FLAKEY, CONFIG_FAIL_MAKE_REQUEST
    • CONFIG_SCSI_DEBUG - fake scsi block device
  • memory
    • CONFIG_SLUB_DEBUG - boot with slub_debug
    • CONFIG_DEBUG_PAGEALLOC + CONFIG_DEBUG_PAGEALLOC_ENABLE_DEFAULT (on newer kernels)
    • CONFIG_PAGE_POISONING
    • CONFIG_HAVE_DEBUG_KMEMLEAK
    • CONFIG_FAILSLAB
  • btrfs
    • CONFIG_BTRFS_DEBUG, CONFIG_BTRFS_ASSERT, CONFIG_BTRFS_FS_RUN_SANITY_TESTS
    • CONFIG_BTRFS_FS_CHECK_INTEGRITY
  • locking
    • CONFIG_DEBUG_SPINLOCK, CONFIG_DEBUG_MUTEXES
    • CONFIG_DEBUG_LOCK_ALLOC
    • CONFIG_PROVE_LOCKING, CONFIG_LOCKDEP
    • CONFIG_LOCK_STAT
    • CONFIG_PROVE_RCU
  • sanity checks
    • CONFIG_DEBUG_STACK_USAGE, CONFIG_HAVE_DEBUG_STACKOVERFLOW, CONFIG_DEBUG_STACKOVERFLOW
    • CONFIG_STACKTRACE
    • kasan
  • verbose reporting
    • CONFIG_DEBUG_BUGVERBOSE
  • tracing
    • CONFIG_TRACING etc

xfstests

xfstests has very few "hard" requirements and will succeed without running many of the tests. In order to ensure full test coverage, your test environment should provide the following.

Kernel config options for complete test coverage

  • CONFIG_FAULT_INJECTION=y
  • CONFIG_FAULT_INJECTION_DEBUG_FS=y
  • CONFIG_FAIL_MAKE_REQUEST=y
  • CONFIG_DM_FLAKEY=m or y
  • CONFIG_BLK_DEV_LOOP=m or y

Kernel config options for better bug reports

See the list in the section above for more options.

User space utilities and development library dependencies

  • fio
  • dmsetup
  • xfsprogs >= 4.3.1
    • xfs_io -c reflink is required.
  • btrfsprogs
  • dbench
  • openssl
  • libacl
  • libattr
  • libaio
  • libuuid

Note: This list may be incomplete.

Storage environment

  • At least 4 identically sized partitions/disks/virtual disks, specified using $SCRATCH_DEV_POOL
    • some tests may require 6 such partitions

Other requirements

  • An fsgqa user and group must exist.
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