</> whyno filesystem flags check

# components

• process check_fs_flags(state)

  checks filesystem flags: immutable and append-only attributes

  ioctlfs/namei.c
• decision resolve target component

  determines which path component in the walk is the check target

• degraded degraded

  walk array too short to identify the target path component

• decision flags probed?

  checks if filesystem flags were successfully read via ioctl

• degraded degraded: can't read flags

  ioctl for flags returned unknown or inaccessible

• decision operation type?

  branches on the requested operation — flags block writes and metadata ops, not reads

• pass pass: flags don't restrict

  read, stat, and execute are never blocked by filesystem flags

• decision immutable?

  checks the immutable flag (chattr +i) on the target file

• fail fail: chattr +i

  write blocked because the target has the immutable attribute

• decision append_only?

  checks the append-only flag (chattr +a) on the target file

• fail fail: chattr +a

  write blocked because the target has the append-only attribute

• pass pass

  no filesystem flags block this write operation

• decision immutable?

  checks the immutable flag on the parent directory

• fail fail: parent has chattr +i

  delete or create blocked because the parent directory is immutable

• decision delete and append_only?

  append-only on parent blocks deletion but allows creation

• fail fail: parent has chattr +a

  deletion blocked because the parent directory has append-only set

• pass pass

  no filesystem flags on the parent block this operation