FROMLIST: fuse: Passthrough initialization and release

Implement the FUSE passthrough ioctl() that associates the lower
(passthrough) file system file with the fuse_file.

The file descriptor passed to the ioctl() by the FUSE daemon is used to
access the relative file pointer, that will be copied to the fuse_file data
structure to consolidate the link between the FUSE and lower file system.

To enable the passthrough mode, userspace triggers the
FUSE_DEV_IOC_PASSTHROUGH_OPEN ioctl() and, if the call succeeds,
receives back an identifier that will be used at open/create response
time in the fuse_open_out field to associate the FUSE file to the lower
file system file.
The value returned by the ioctl() to userspace can be:
- > 0: success, the identifier can be used as part of an open/create
  reply.
- < 0: an error occurred.
The value 0 has been left unused for backward compatibility: the
fuse_open_out field that is used to pass the passthrough_fh back to the
kernel uses the same bits that were previously as struct padding,
zero-initialized in the common libfuse implementation. Removing the 0
value fixes the ambiguity between the case in which 0 corresponds to a
real passthrough_fh or a missing implementation, simplifying the
userspace implementation.

For the passthrough mode to be successfully activated, the lower file
system file must implement both read_ and write_iter file operations.
This extra check avoids special pseudo files to be targeted for this
feature.
Passthrough comes with another limitation: no further file system stacking
is allowed for those FUSE file systems using passthrough.

Bug: 168023149
Link: https://lore.kernel.org/lkml/20201026125016.1905945-3-balsini@android.com/
Signed-off-by: Alessio Balsini <balsini@android.com>
Signed-off-by: Alessio Balsini <balsini@google.com>
Change-Id: Id6067dcb882d58daef5ffe44355c383cabeed547
2 files changed
tree: 1e2f9f48e67553089338d8575c961231acca8ff5
  1. arch/
  2. block/
  3. certs/
  4. crypto/
  5. Documentation/
  6. drivers/
  7. fs/
  8. include/
  9. init/
  10. ipc/
  11. kernel/
  12. lib/
  13. LICENSES/
  14. mm/
  15. net/
  16. samples/
  17. scripts/
  18. security/
  19. sound/
  20. tools/
  21. usr/
  22. virt/
  23. .clang-format
  24. .cocciconfig
  25. .get_maintainer.ignore
  26. .gitattributes
  27. .gitignore
  28. .mailmap
  29. build.config.aarch64
  30. build.config.allmodconfig
  31. build.config.allmodconfig.aarch64
  32. build.config.allmodconfig.arm
  33. build.config.allmodconfig.x86_64
  34. build.config.arm
  35. build.config.common
  36. build.config.db845c
  37. build.config.gki
  38. build.config.gki-debug.aarch64
  39. build.config.gki-debug.x86_64
  40. build.config.gki.aarch64
  41. build.config.gki.x86_64
  42. build.config.gki_kasan
  43. build.config.gki_kasan.aarch64
  44. build.config.gki_kasan.x86_64
  45. build.config.x86_64
  46. COPYING
  47. CREDITS
  48. Kbuild
  49. Kconfig
  50. MAINTAINERS
  51. Makefile
  52. README
  53. README.md
README.md

How do I submit patches to Android Common Kernels

  1. BEST: Make all of your changes to upstream Linux. If appropriate, backport to the stable releases. These patches will be merged automatically in the corresponding common kernels. If the patch is already in upstream Linux, post a backport of the patch that conforms to the patch requirements below.

    • Do not send patches upstream that contain only symbol exports. To be considered for upstream Linux, additions of EXPORT_SYMBOL_GPL() require an in-tree modular driver that uses the symbol -- so include the new driver or changes to an existing driver in the same patchset as the export.
    • When sending patches upstream, the commit message must contain a clear case for why the patch is needed and beneficial to the community. Enabling out-of-tree drivers or functionality is not not a persuasive case.
  2. LESS GOOD: Develop your patches out-of-tree (from an upstream Linux point-of-view). Unless these are fixing an Android-specific bug, these are very unlikely to be accepted unless they have been coordinated with kernel-team@android.com. If you want to proceed, post a patch that conforms to the patch requirements below.

Common Kernel patch requirements

  • All patches must conform to the Linux kernel coding standards and pass script/checkpatch.pl
  • Patches shall not break gki_defconfig or allmodconfig builds for arm, arm64, x86, x86_64 architectures (see https://source.android.com/setup/build/building-kernels)
  • If the patch is not merged from an upstream branch, the subject must be tagged with the type of patch: UPSTREAM:, BACKPORT:, FROMGIT:, FROMLIST:, or ANDROID:.
  • All patches must have a Change-Id: tag (see https://gerrit-review.googlesource.com/Documentation/user-changeid.html)
  • If an Android bug has been assigned, there must be a Bug: tag.
  • All patches must have a Signed-off-by: tag by the author and the submitter

Additional requirements are listed below based on patch type

Requirements for backports from mainline Linux: UPSTREAM:, BACKPORT:

  • If the patch is a cherry-pick from Linux mainline with no changes at all
    • tag the patch subject with UPSTREAM:.
    • add upstream commit information with a (cherry picked from commit ...) line
    • Example:
      • if the upstream commit message is
        important patch from upstream

        This is the detailed description of the important patch

        Signed-off-by: Fred Jones <fred.jones@foo.org>
  • then Joe Smith would upload the patch for the common kernel as
        UPSTREAM: important patch from upstream

        This is the detailed description of the important patch

        Signed-off-by: Fred Jones <fred.jones@foo.org>

        Bug: 135791357
        Change-Id: I4caaaa566ea080fa148c5e768bb1a0b6f7201c01
        (cherry picked from commit c31e73121f4c1ec41143423ac6ce3ce6dafdcec1)
        Signed-off-by: Joe Smith <joe.smith@foo.org>
  • If the patch requires any changes from the upstream version, tag the patch with BACKPORT: instead of UPSTREAM:.
    • use the same tags as UPSTREAM:
    • add comments about the changes under the (cherry picked from commit ...) line
    • Example:
        BACKPORT: important patch from upstream

        This is the detailed description of the important patch

        Signed-off-by: Fred Jones <fred.jones@foo.org>

        Bug: 135791357
        Change-Id: I4caaaa566ea080fa148c5e768bb1a0b6f7201c01
        (cherry picked from commit c31e73121f4c1ec41143423ac6ce3ce6dafdcec1)
        [joe: Resolved minor conflict in drivers/foo/bar.c ]
        Signed-off-by: Joe Smith <joe.smith@foo.org>

Requirements for other backports: FROMGIT:, FROMLIST:,

  • If the patch has been merged into an upstream maintainer tree, but has not yet been merged into Linux mainline
    • tag the patch subject with FROMGIT:
    • add info on where the patch came from as (cherry picked from commit <sha1> <repo> <branch>). This must be a stable maintainer branch (not rebased, so don't use linux-next for example).
    • if changes were required, use BACKPORT: FROMGIT:
    • Example:
      • if the commit message in the maintainer tree is
        important patch from upstream

        This is the detailed description of the important patch

        Signed-off-by: Fred Jones <fred.jones@foo.org>
  • then Joe Smith would upload the patch for the common kernel as
        FROMGIT: important patch from upstream

        This is the detailed description of the important patch

        Signed-off-by: Fred Jones <fred.jones@foo.org>

        Bug: 135791357
        (cherry picked from commit 878a2fd9de10b03d11d2f622250285c7e63deace
         https://git.kernel.org/pub/scm/linux/kernel/git/foo/bar.git test-branch)
        Change-Id: I4caaaa566ea080fa148c5e768bb1a0b6f7201c01
        Signed-off-by: Joe Smith <joe.smith@foo.org>
  • If the patch has been submitted to LKML, but not accepted into any maintainer tree
    • tag the patch subject with FROMLIST:
    • add a Link: tag with a link to the submittal on lore.kernel.org
    • add a Bug: tag with the Android bug (required for patches not accepted into a maintainer tree)
    • if changes were required, use BACKPORT: FROMLIST:
    • Example:
        FROMLIST: important patch from upstream

        This is the detailed description of the important patch

        Signed-off-by: Fred Jones <fred.jones@foo.org>

        Bug: 135791357
        Link: https://lore.kernel.org/lkml/20190619171517.GA17557@someone.com/
        Change-Id: I4caaaa566ea080fa148c5e768bb1a0b6f7201c01
        Signed-off-by: Joe Smith <joe.smith@foo.org>

Requirements for Android-specific patches: ANDROID:

  • If the patch is fixing a bug to Android-specific code
    • tag the patch subject with ANDROID:
    • add a Fixes: tag that cites the patch with the bug
    • Example:
        ANDROID: fix android-specific bug in foobar.c

        This is the detailed description of the important fix

        Fixes: 1234abcd2468 ("foobar: add cool feature")
        Change-Id: I4caaaa566ea080fa148c5e768bb1a0b6f7201c01
        Signed-off-by: Joe Smith <joe.smith@foo.org>
  • If the patch is a new feature
    • tag the patch subject with ANDROID:
    • add a Bug: tag with the Android bug (required for android-specific features)