x/sys/unix: add support for FAN_REPORT_FID

[s3rj1k]

Linux kernels 5.1+ have added new API (FAN_REPORT_FID) for fanotify. Would be nice to have this in 'golang.org/x/sys'.

[ianlancetaylor]

Want to send a patch?

[tklauser]

The const is already there since https://golang.org/cl/175158:

zerrors_linux_386.go:677:       FAN_REPORT_FID                       = 0x200
zerrors_linux_amd64.go:677:     FAN_REPORT_FID                       = 0x200
zerrors_linux_arm.go:677:       FAN_REPORT_FID                       = 0x200
zerrors_linux_arm64.go:679:     FAN_REPORT_FID                       = 0x200
zerrors_linux_mips.go:677:      FAN_REPORT_FID                       = 0x200
zerrors_linux_mips64.go:677:    FAN_REPORT_FID                       = 0x200
zerrors_linux_mips64le.go:677:  FAN_REPORT_FID                       = 0x200
zerrors_linux_mipsle.go:677:    FAN_REPORT_FID                       = 0x200
zerrors_linux_ppc64.go:677:     FAN_REPORT_FID                       = 0x200
zerrors_linux_ppc64le.go:677:   FAN_REPORT_FID                       = 0x200
zerrors_linux_riscv64.go:677:   FAN_REPORT_FID                       = 0x200
zerrors_linux_s390x.go:677:     FAN_REPORT_FID                       = 0x200
zerrors_linux_sparc64.go:681:   FAN_REPORT_FID                       = 0x200

Is there anything else needed to use this API?

[s3rj1k]

@tklauser @ianlancetaylor Hi all. Yes not all structures are present and there is no helper func to get fanotify events.
I was using code that looks hacky, not written by my, have no idea how to rewrite it.
Code is located here https://github.com/ozeidan/gosearch/blob/master/internal/fanotify/fanotify.go

The structs are needed:

• fanotifyInfoHeader
• fileHandle, using the one in unix brakes the code
• fanotifyEventFid
• fanotifyEventInfoFid

A function that can read this structs from a memory, the unsafe magic and reaf buffers,
Results of that function then can be passed to unix.NewFileHandle and unix.OpenByHandleAt.

Initial unix.FanotifyEventMetadata can be read with binary.Read, for example like this.

The problem lies with extra structs that come after initial unix.FanotifyEventMetadata then fanotify is used with FAN_REPORT_FID flag. This structs can have offset (padding) and part of this struct needs to be passed to unix.OpenByHandleAt to get FD of a opened fanotify file.

All of this looks quite a challenge at least for me :)