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JDK-8030048: (fs) Support UserDefinedFileAttributeView/extended attributes on OS X / HFS+ #2017

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@overheadhunter overheadhunter commented Jan 10, 2021

This adds support for UserDefinedFileAttributeView on macOS 10.4 and newer.

While the main audience for this will probably be macOS users, the relevant changes take place in (mostly existing) classes carrying BSD in their names as none of this is really macOS-specific.

Code is mostly copied from the Linux implementation except for three differences:

  1. max length for attribute names is 127 bytes
  2. we know for sure that APFS and HFS+ support extended attributes, therefore we simply return true from supportsFileAttributeView(UserDefinedFileAttributeView.class) for these two FS types, while for all other types support is determined experimentally in isExtendedAttributesEnabled(...)
  3. For the aforementioned check the new UnixConstants.ENOATTR is added, which seems to be macOS and BSD-specific.

As discussed in the mailing list, for ease of tracking changes it is not a goal of this patch to modernize the existing Linux implementation, nor to deduplicate anything.


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  • JDK-8030048: (fs) Support UserDefinedFileAttributeView/extended attributes on OS X / HFS+

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$ git fetch https://git.openjdk.java.net/jdk pull/2017/head:pull/2017
$ git checkout pull/2017

@bridgekeeper bridgekeeper bot added the oca Needs verification of OCA signatory status label Jan 10, 2021
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Hi @overheadhunter, welcome to this OpenJDK project and thanks for contributing!

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@overheadhunter The following label will be automatically applied to this pull request:

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@openjdk openjdk bot added the nio nio-dev@openjdk.org label Jan 10, 2021
@overheadhunter overheadhunter changed the title JDK-8030048 Add macOS support for UserDefinedFileAttributeView JDK-8030048: (fs) Support UserDefinedFileAttributeView/extended attributes on OS X / HFS+ Jan 10, 2021
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overheadhunter commented Jan 10, 2021

/covered This patch is submitted on behalf of Skymatic GmbH, for whom I've recently sent in the signed OCA.

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/covered

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@bridgekeeper bridgekeeper bot removed oca Needs verification of OCA signatory status oca-verify Needs verification of OCA signatory status labels Jan 11, 2021
@openjdk openjdk bot added the rfr Pull request is ready for review label Jan 11, 2021
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Webrevs

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Overall, this looks quite good and is easy to review.

I think the additions to BsdNativeDispatcher. will need a round or two of cleanup. They comments about XATTR_NOFOLLOW and other options documented in the man pages are a bit distracting. Also the style and excessive long lines aren't consistent with the existing code (and UnixNativeDispatcher).

One thing that we need to decide is whether the additional parameters (position, options) are exposed by BsdNativeDispatcher or not. I think I agree with your approach to have the signature match the methods in LinuxNativeDispatcher as that will make it easier to merge the two implementations later.

The comments that XATTR_NOFOLLOW is not applicable and other options not used is distracting and can be removed.

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overheadhunter commented Jan 13, 2021

One thing that we need to decide is whether the additional parameters (position, options) are exposed by BsdNativeDispatcher or not. I think I agree with your approach to have the signature match the methods in LinuxNativeDispatcher as that will make it easier to merge the two implementations later.

Just to discuss all options, we could as well hide both params from Java entirely (set them inside of BsdNativeDispatcher.c)

The comments that XATTR_NOFOLLOW is not applicable and other options not used is distracting and can be removed.

Sure, but maybe it should be documented somewhere that none of the flags are required for this use case? Or do you think it is reasonable to assume that anyone stumbling upon this code will just look up the system calls' documentation to see what flags might have been possible?

that don't provide any insights not available on the native methods' man pages
(matching format in LinuxNativeDispatcher.java)
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Thanks for the updates. I can sponsor once, you'll need to enter "/integrate"

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openjdk bot commented Jan 15, 2021

@overheadhunter This change now passes all automated pre-integration checks.

ℹ️ This project also has non-automated pre-integration requirements. Please see the file CONTRIBUTING.md for details.

After integration, the commit message for the final commit will be:

8030048: (fs) Support UserDefinedFileAttributeView/extended attributes on OS X / HFS+

Reviewed-by: alanb

You can use pull request commands such as /summary, /contributor and /issue to adjust it as needed.

At the time when this comment was updated there had been 147 new commits pushed to the master branch:

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As you do not have Committer status in this project an existing Committer must agree to sponsor your change. Possible candidates are the reviewers of this PR (@AlanBateman) but any other Committer may sponsor as well.

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@openjdk openjdk bot added the ready Pull request is ready to be integrated label Jan 15, 2021
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/integrate

@openjdk openjdk bot added the sponsor Pull request is ready to be sponsored label Jan 15, 2021
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openjdk bot commented Jan 15, 2021

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Your change (at version 9258c37) is now ready to be sponsored by a Committer.

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mlbridge bot commented Jan 15, 2021

Mailing list message from Sebastian Stenzel on nio-dev:

Thank you, Alan, for guiding me through the process and reviewing the changes!

Regarding the deduplication I already have some ideas and questions, but I think I'll do this in a new thread in a couple of days.

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/integrate

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openjdk bot commented Jan 16, 2021

@AlanBateman Only the author (@overheadhunter) is allowed to issue the integrate command. As this PR is ready to be sponsored, and you are an eligible sponsor, did you mean to issue the /sponsor command?

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/sponsor

@openjdk openjdk bot closed this Jan 16, 2021
@openjdk openjdk bot added integrated Pull request has been integrated and removed sponsor Pull request is ready to be sponsored ready Pull request is ready to be integrated rfr Pull request is ready for review labels Jan 16, 2021
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openjdk bot commented Jan 16, 2021

@AlanBateman @overheadhunter Since your change was applied there have been 152 commits pushed to the master branch:

Your commit was automatically rebased without conflicts.

Pushed as commit afd3f78.

💡 You may see a message that your pull request was closed with unmerged commits. This can be safely ignored.

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Mailing list message from Alan Bateman on nio-dev:

On 15/01/2021 20:19, Sebastian Stenzel wrote:

:
Thank you, Alan, for guiding me through the process and reviewing the changes!

Regarding the deduplication I already have some ideas and questions, but I think I'll do this in a new thread in a couple of days.

No problem, it's a good contribution for something that the maintainers
in this area never got time to work on.

One issue is that has come up since the commit is that
UserDefinedFileAttributeView/Basic.java is failing on macOS 10.13
systems. I've created JDK-8259865 [1] to track it. I can't duplicate it
on 10.14 and 10.15. I think the issue is that fgetxattr is not failing
with -1/ERANGE when the buffer is too small. We may have to disable
support for user defined file attributes on systems older than 10.14.

-Alan

[1] https://bugs.openjdk.java.net/browse/JDK-8259865

@overheadhunter overheadhunter deleted the feature/macos-xattr branch Jan 17, 2021
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