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    SubjectRe: [Qemu-devel] d_off field in struct dirent and 32-on-64 emulation
    On Sat, Dec 29, 2018 at 12:12:27AM +0000, Peter Maydell wrote:
    > On Fri, 28 Dec 2018 at 23:16, Andreas Dilger <adilger@dilger.ca> wrot
    > > On Dec 28, 2018, at 4:18 AM, Peter Maydell <peter.maydell@linaro.org> wrote:
    > > > The problem is that there is no 32-bit API in some cases
    > > > (unless I have misunderstood the kernel code) -- not all
    > > > host architectures implement compat syscalls or allow them
    > > > to be called from 64-bit processes or implement all the older
    > > > syscall variants that had smaller offets. If there was a guaranteed
    > > > "this syscall always exists and always gives me 32-bit offsets"
    > > > we could use it.
    > >
    > > The "32bitapi" mount option would use 32-bit hash for seekdir
    > > and telldir, regardless of what kernel API was used. That would
    > > just set the FMODE_32BITHASH flag in the file->f_mode for all files.
    >
    > A mount option wouldn't be much use to QEMU -- we can't tell
    > our users how to mount their filesystems, which they're
    > often doing lots of other things with besides running QEMU.
    > (Otherwise we could just tell them "don't use ext4", which
    > would also solve the problem :-)) We need something we can
    > use at the individual-syscall level.

    Could you use a prctl to set whether you were running in 32 or 64 bit
    mode? Or do you change which kind of task you're emulating too often
    to make this a good idea?

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