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Date: Sat, 22 Aug 2015 23:17:18 +0200 From: Richard Cochran <richardcochran@...il.com> To: Thomas Gleixner <tglx@...utronix.de> Cc: "Christopher S. Hall" <christopher.s.hall@...el.com>, jeffrey.t.kirsher@...el.com, hpa@...or.com, mingo@...hat.com, john.stultz@...aro.org, x86@...nel.org, linux-kernel@...r.kernel.org, netdev@...r.kernel.org, intel-wired-lan@...ts.osuosl.org, peterz@...radead.org Subject: Re: [PATCH v3 3/4] Add support for driver cross-timestamp to PTP_SYS_OFFSET ioctl On Sat, Aug 22, 2015 at 10:33:48PM +0200, Thomas Gleixner wrote: > > @@ -196,19 +197,31 @@ long ptp_ioctl(struct posix_clock *pc, unsigned int cmd, unsigned long arg) > > break; > > } > > pct = &sysoff->ts[0]; > > - for (i = 0; i < sysoff->n_samples; i++) { > > - getnstimeofday64(&ts); > > + if (ptp->info->getsynctime64 && sysoff->n_samples == 1 && > > The number of samples should be irrelevant for this sampling method. Chris had send me a preview of this before he posted, so I can explain that test for one sample. User space requests N (1 to 25) samples of the two clocks. The kernel is supposed to deliver that many samples. This has always been the documented behavior. From ptp_clock.h: struct ptp_sys_offset { unsigned int n_samples; /* Desired number of measurements. */ unsigned int rsv[3]; /* Reserved for future use. */ /* * Array of interleaved system/phc time stamps. The kernel * will provide 2*n_samples + 1 time stamps, with the last * one as a system time stamp. */ struct ptp_clock_time ts[2 * PTP_MAX_SAMPLES + 1]; }; So the kernel cannot simply change n_samples to 1. I would prefer to have a new system call that compares any two posix clock_t, but that is of course more work. Allowing n_samples=1 as a special case is a kind of overloading of the ioctl to support the new capability. At least it preserves the behavior of the interface from the user's perspective. Thanks, Richard -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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