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

From: Michael Roitzsch
Subject: Re: [PATCH v2 04/11] 9p: darwin: Handle struct dirent differences
Date: Wed, 24 Nov 2021 16:45:30 +0100


> 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);
        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.

This is on Monterey. Unfortunately I cannot test if older versions of macOS are 


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