RHEL-8 file create #199
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RHEL-8 file create #199
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nicholasberlin
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On RHEL kernels where ebpf has been backported but FMODE_CREATED does not yet exist, use fsnotify_create as an indication of file creation. This requires a new probe to set a thread local map entry, which the current do_filp_open probe can then test for.
Since the fsnotify probe can be noisy and the parameters have changed over time, only enable that probe when necessary. Ideally, we would test for the existence of FMODE_CREATED, but as far as I'm aware, there's not a way to detect defines. There's another commit (torvalds/linux@44907d7) related to the addition of FMODE_CREATED which is detectable by testing the parameter count to the atomic_open function pointer within struct inode_operations. This commit adds a function to detect the commit using btf, and conditionally adds the fsnotify probe.
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Awesome, this is great thanks! |
haesbaert
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Jun 30, 2025
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On RHEL kernels where ebpf has been back-ported but
FMODE_CREATEDdoes not yet exist, usefsnotify_createas an indication of file creation. This requires a new probe onfsnotifyto set a thread local map entry, which the currentdo_filp_openexit probe can then test for.Since the
fsnotifyprobe can be noisy and the parameters have changed over time, onlyenable that probe when necessary. Ideally, we would test for the existence of
FMODE_CREATED, but as far as I'm aware, there's not a way to detect#defines. There's another commit (torvalds/linux@44907d7) relatedto the addition of
FMODE_CREATEDwhich is detectable by testing the parameter count of theatomic_openfunction pointer withinstruct inode_operations.A new function was added to use btf for detecting the parameter change, and is used to conditionally apply the
fnsotifyprobe. Hopefully, the parameter count toatomic_openwill not change back to 6.Also, re-enabled file testing for the appropriate kernels.
Thanks @haesbaert for the feedback/review. I incorporated and squashed this and this.