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Re: Linux Extended-stat system call


On 06/22/2016 06:03 PM, Arnd Bergmann wrote:
On Wednesday, June 22, 2016 5:03:43 PM CEST Florian Weimer wrote:
On 06/22/2016 04:08 PM, David Howells wrote:

One thing I would like to do is make it so that stat() can use it with minimal
effort.

Why is this an important goal?

Existing architectures will keep using the old system call for the
legacy stat interfaces.  New architectures can use the new system call,
but will probably have a different definition of struct stat (which
might well be guided by our experience with the extended stat interface).

For the y2038 work, we have to replace the stat system call on all 32-bit
architectures (and mips64, which uses 32-bit st_mtime). We can do this
by adding just a new version of the fstatat() syscall to the kernel that
matches the ABI of the 64-bit architectures, or by mapping everything
onto the new xstat.

Adding just one new syscall entry point instead of two simplifies the
kernel implementation quite a bit, but if there are good reasons for
still providing a new fstatat version, we could do that too.

Thanks for providing the background.

If we can get all the data with a single system call, I don't think it matters much were we do the translation. A single new system call is less work for strace, so I assume that's the way to go.

Florian


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