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SubjectRe: [PATCH 1/4] Cache xattr security drop check for write
On Fri, May 27, 2011 at 03:54:02PM -0700, Andi Kleen wrote:
> From: Andi Kleen <ak@linux.intel.com>
>
> Some recent benchmarking on btrfs showed that a major scaling bottleneck
> on large systems on btrfs is currently the xattr lookup on every write.
>
> Why xattr lookup on every write I hear you ask?
>
> write wants to drop suid and security related xattrs that could set o
> capabilities for executables. To do that it currently looks up
> security.capability on EVERY write (even for non executables) to decide
> whether to drop it or not.

Hm...
a) is_sgid() is a bad name for that - at the very least s/g/x/, since
anybody would read your variant as "check if it's set-group-id".
b) I'd add a helper for filesystems to use, rather than messing
with the flags directly.


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