Re: [PATCH v2 04/11] 9p: darwin: Handle struct dirent differences

[Will Cohen]

If acceptable, we'd still propose leaving these changes as is for expediency's sake, rather than using our dirent and then translating it all to save one read from the FS layer.

For v3, the synth tests will pass. We did have to modify the local fs_unlinkat_dir test to correct AT_REMOVEDIR to P9_DOTL_AT_REMOVEDIR to get that test to pass, but those now pass as well.

On Wed, Nov 24, 2021 at 2:09 PM Christian Schoenebeck <qemu_oss@crudebyte.com> wrote:

On Mittwoch, 24. November 2021 16:45:30 CET Michael Roitzsch wrote:
> Hi,
>
> > Are you sure d_seekoff doesn't work on macOS?
>
> I just tried on an APFS volume on macOS Monterey and d_seekoff is always 0,
> while telldir() outputs useful values.
> > Because using telldir() instead
> > is not the same thing. Accessing d_*off is just POD access, whereas
> > telldir() is a syscall.
>
> I am not sure this is the case. I have tried a quick test program:
>
> #include <dirent.h>
>
> int main(void)
> {
>       int result = 0;
>       DIR *dir = opendir(".");
>       while (readdir(dir)) {
>               result += telldir(dir);
>       }
>       closedir(dir);
>       return result;
> }
>
> I ran it with 'sudo dtruss ./test', which should give me a trace of the
> system calls. The relevant portion is:
>
> open_nocancel(".\0", 0x1100004, 0x0)           = 3 0
> sysctlbyname(kern.secure_kernel, 0x12, 0x7FF7BE49810C, 0x7FF7BE498110,
> 0x0)           = 0 0 fstatfs64(0x3, 0x7FF7BE498110, 0x0)               = 0 0
> getdirentries64(0x3, 0x7FF4A5808A00, 0x2000)           = 1472 0
> close_nocancel(0x3)            = 0 0
>
> The directory has more than 30 entries, but the loop does not appear to
> cause individual system calls. Instead, readdir() and telldir() appear to
> be library functions powered by this getdirentries64 syscall.

Right, telldir() is part of Apple's libc, no (fs) syscall involved:
https://opensource.apple.com/source/Libc/Libc-167/gen.subproj/telldir.c.auto.html

However instead of changing the (fs driver independent) 9p server [9p.c] code
and using fidp there, I would probably rather address this issue for macOS in
the individual fs drivers [9p-local.c, 9p-synth.c, 9p-proxy.c] directly on
dirent instead, and not rely on fidp not having mutated on server.

And please make sure the 9p test cases pass.

Best regards,
Christian Schoenebeck