Development notes

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* At least 4 identically sized partitions/disks/virtual disks, specified using <code>$SCRATCH_DEV_POOL</code>
 
* At least 4 identically sized partitions/disks/virtual disks, specified using <code>$SCRATCH_DEV_POOL</code>
 
** some tests may require 6 such partitions
 
** some tests may require 6 such partitions
 +
* some tests need at least 10G of free space, as determined by <code>df</code>, ie. the size of the device may need to be larger
  
 
== Other requirements ==
 
== Other requirements ==
 
* An <code>fsgqa</code> user and group must exist.
 
* An <code>fsgqa</code> user and group must exist.
 
* An <code>123456-fsgqa</code> user and group must exist.
 
* An <code>123456-fsgqa</code> user and group must exist.

Revision as of 16:16, 14 February 2019

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)
  • use struct btrfs_inode for inode types, not plain struct inode
  • inode number type is u64, use btrfs_ino if needed
  • key can be printed as [%llu,%u,%llu]
  • enum types need to be exported as TRACE_DEFINE_ENUM

Example:

event: btrfs__chunk

string:

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

Error messages, verbosity

  • use btrfs_* helpers (btrfs_err, btrfs_info, ...), they print a filesystem identification like
BTRFS info (device sdb): ...
  • first letter in the string is lowercase
  • message contents
    • be descriptive
    • keep the text length reasonable (fits one line without wrapping)
    • no typos
    • print values that refer to what happend (inode number, subvolume id, path, offset, ...)
    • print error value from the last call
    • no "\n" at the end of the string
    • no ".'' at the end of text
    • un-indent the string so it fits under 80 columns
    • don't split long strings, overflow 80 is ok in this case (we want to be able to search for the error messages in the sources easily)

Message level

  • btrfs_err -- such messages have high visibility so use them for serious problems that need user attention
  • btrfs_warn -- conditions that are not too serious but can point to potential problems, the system should be still in a good state
  • btrfs_info -- use for informative messages that are useful to see what's happening in the filesystem or might help debugging problems in the future and are worth keeping in the logs

Error handling and transaction abort

Please keep all transaction abort exactly at the place where they happen and do not merge them to one. This pattern should be used everwhere and is important when debugging because we can pinpoint the line in the code from the syslog message and do not have to guess which way it got to the merged call.

BCP

  • do not use spin_is_locked but lockdep_assert_held

Coding style preferences

Before applying recommendations from this sections, please make sure you're familiar with the kernel coding style guide.

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

(x)fstests

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_DM_THIN_PROVISIONING=m or y
  • CONFIG_DM_SNAPSHOT=m or y
  • CONFIG_DM_DELAY=m or y
  • CONFIG_DM_ERROR=m or y
  • CONFIG_DM_LOG_WRITES=m or y
  • CONFIG_BLK_DEV_LOOP=m or y
  • CONFIG_EXT4_FS=m or y
  • CONFIG_SCSI_DEBUG=m

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
  • some tests need at least 10G of free space, as determined by df, ie. the size of the device may need to be larger

Other requirements

  • An fsgqa user and group must exist.
  • An 123456-fsgqa user and group must exist.
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