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tracing/uprobe: Add support for overlayfs
uprobes cannot successfully attach to binaries located in a directory mounted with overlayfs. To verify, create directories for mounting overlayfs (upper,lower,work,merge), move some binary into merge/ and use readelf to obtain some known instruction of the binary. I used /bin/true and the entry instruction(0x13b0): $ mount -t overlay overlay -o lowerdir=lower,upperdir=upper,workdir=work merge $ cd /sys/kernel/debug/tracing $ echo 'p:true_entry PATH_TO_MERGE/merge/true:0x13b0' > uprobe_events $ echo 1 > events/uprobes/true_entry/enable This returns 'bash: echo: write error: Input/output error' and dmesg tells us 'event trace: Could not enable event true_entry' This change makes create_trace_uprobe() look for the real inode of a dentry. In the case of normal filesystems, this simplifies to just returning the inode. In the case of overlayfs(and similar fs) we will obtain the underlying dentry and corresponding inode, upon which uprobes can successfully register. Running the example above with the patch applied, we can see that the uprobe is enabled and will output to trace as expected. Link: http://firstname.lastname@example.org Reviewed-by: Josef Bacik <email@example.com> Reviewed-by: Masami Hiramatsu <firstname.lastname@example.org> Reviewed-by: Srikar Dronamraju <email@example.com> Signed-off-by: Howard McLauchlan <firstname.lastname@example.org> Signed-off-by: Steven Rostedt (VMware) <email@example.com>
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