Ulrich Drepper <[email protected]> wrote:
> In sys_faccessat you temporarily allocate a cred object which is
> discarded in the end. With a few more macro definitions you could
> create a dup_cred variant which initialized an automatic variable of
> type struct cred. This way the kmalloc/kfree pair would fall away.
No, you can't. The filesystems sys_faccessat() then invokes are entitled to
take a reference to it - the SunRPC authentication stuff, for example - so you
can't just preemptively unallocate it as would occur with an automatic variable.
> access is actually used frequently. For instance, ld.so uses it on
> every startup as a quicker possibility to check for a file which
> usually doesn't exist. So, speeding up access has some small effect
> on performance. The resulting code might actually reduce the kernel
> size a bit due to all the checks and calls which go away.
A better way would be to compare fsuid/fsgid to uid/gid and to just take an
extra ref on the incumbent cred object if they're the same, rather than always
allocating a new one. That, I suspect, would speed up 99.99% of the cases.
David
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