November 2014 - Darwin-kernel

Re: file changes content but ContentModificationDate not changing
by Gerriet M. Denkmann 06 Nov '14

06 Nov '14

> On 5 Nov 2014, at 23:47, Quinn The Eskimo! <eskimo1(a)apple.com> wrote: > > On 5 Nov 2014, at 16:43, Gerriet M. Denkmann <gerriet(a)mdenkmann.de> wrote: > >> On 5 Nov 2014, at 20:31, Quinn The Eskimo! <eskimo1(a)apple.com> wrote: >> >>> It [i.e. the inode] should change each time the file is saved. >> >> It should, but it does not. > > Curious. Alas, the source for ntpd is complex enough that I may be looking at completely the wrong code. On option here is to use fs_usage to see what system calls ntpd is using to make this change and track things from there. Following your advice I found a way to change a file without DISPATCH_SOURCE_TYPE_VNODE noticing it (same way save_drift_file() in ntp_util.c does it): static void *mmap_addr; static off_t stats_size; if ( mmap_addr == NULL ) { // will receive DISPATCH_VNODE_ATTRIB (sometimes twice) NSLog(@"%s will write %g (case 2: setting mmap_addr)",__FUNCTION__, drift_comp * 1e6); int fd = open(stats_drift_file, O_RDWR); if ( fd < 0 ) ... // error mmap_addr = mmap(0, pageSize, PROT_READ|PROT_WRITE, MAP_FILE|MAP_SHARED, fd, 0); if (mmap_addr == MAP_FAILED) ... // error off_t n = snprintf(mmap_addr, pageSize, "%.3f\n", drift_comp * 1e6); if (n != stats_size) { truncate(stats_drift_file, n); stats_size = n; }; close(fd); } else // stealth-mode { // will receive no DISPATCH_VNODE_XXX at all // does NOT update the change-time of stats_drift_file NSLog(@"%s will write %g (case 3: stealth-mode using mmap)",__FUNCTION__, drift_comp * 1e6); off_t n = snprintf(mmap_addr, pageSize, "%.3f\n", drift_comp * 1e6); if (n != stats_size) // size of ntp.drift changed { truncate(stats_drift_file, n); stats_size = n; }; }; Question: is this the way it should be? Or is this stealth-mode a bug? Kind regards, Gerriet. _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-kernel mailing list (Darwin-kernel(a)lists.apple.com) Help/Unsubscribe/Update your Subscription: https://lists.apple.com/mailman/options/darwin-kernel/site_archiver%40lists… This email sent to site_archiver(a)lists.apple.com

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Core Storage read/write request
by p p 05 Nov '14

05 Nov '14

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Re: Timing / Scheduling issues / screensaver
by Jean Suisse 05 Nov '14

05 Nov '14

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Re: file changes content but ContentModificationDate not changing
by Quinn "The Eskimo!" 05 Nov '14

05 Nov '14

On 5 Nov 2014, at 16:43, Gerriet M. Denkmann <gerriet(a)mdenkmann.de> wrote: > On 5 Nov 2014, at 20:31, Quinn The Eskimo! <eskimo1(a)apple.com> wrote: > >> It [i.e. the inode] should change each time the file is saved. > > It should, but it does not. Curious. Alas, the source for ntpd is complex enough that I may be looking at completely the wrong code. On option here is to use fs_usage to see what system calls ntpd is using to make this change and track things from there. Share and Enjoy -- Quinn "The Eskimo!" <http://www.apple.com/developer/> Apple Developer Relations, Developer Technical Support, Core OS/Hardware _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-kernel mailing list (Darwin-kernel(a)lists.apple.com) Help/Unsubscribe/Update your Subscription: https://lists.apple.com/mailman/options/darwin-kernel/site_archiver%40lists… This email sent to site_archiver(a)lists.apple.com

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Re: file changes content but ContentModificationDate not changing
by Gerriet M. Denkmann 05 Nov '14

05 Nov '14

Send again - this time with correct From: > On 5 Nov 2014, at 20:31, Quinn The Eskimo! <eskimo1(a)apple.com> wrote: > > > On 5 Nov 2014, at 13:13, Gerriet M. Denkmann <gerriet(a)mdenkmann.de> wrote: > >> Any way to observe changes (except from polling, which I am trying to avoid)? > > AFAICT ntpd doesn't write to this file, but rather writes to a temporary file and then replaces the original file with a temporary (using <x-man-page://2/rename>). This is a pretty typical 'safe save' technique. > > See save_drift_file in the following. > > <http://www.opensource.apple.com/source/ntp/ntp-92/ntpd/ntp_util.c> Ok. But when I observe some other file using dispatch_source_create(DISPATCH_SOURCE_TYPE_VNODE) and do a rename, I get a DISPATCH_VNODE_DELETE or DISPATCH_VNODE_RENAME. With ntp.drift I see nothing at all (most of the time). > > You can confirm this by checking the inode number of the file over time. > > $ ls -li /var/db/ntp.drift > 9615173 -rw-r--r-- 1 root wheel 9 4 Nov 09:46 /var/db/ntp.drift $ date; ls -li /var/db/ntp.drift ; cat /var/db/ntp.drift Wed 5 Nov 2014 21:16:52 ICT 5424511 -rw-r--r--@ 1 root wheel 8 5 Nov 14:59 /var/db/ntp.drift <-- change-time unchanged for 6 hours -20.410 -- wait -- $ date; ls -li /var/db/ntp.drift ; cat /var/db/ntp.drift Wed 5 Nov 2014 21:21:39 ICT 5424511 -rw-r--r--@ 1 root wheel 8 5 Nov 21:21 /var/db/ntp.drift ← inode did NOT change -20.430 ← data did change This is a rare and bad example, because the change-time did actually change. And so I received two DISPATCH_VNODE_ATTRIB events. -- wait another hour -- $ date; ls -li /var/db/ntp.drift ; cat /var/db/ntp.drift Wed 5 Nov 2014 22:25:47 ICT 5424511 -rw-r--r--@ 1 root wheel 8 5 Nov 21:21 /var/db/ntp.drift ← inode did NOT change, nor did change-time -20.434 ← data did change > > It [i.e. the inode] should change each time the file is saved. It should, but it does not. > > If this is, indeed, how things work, you'll have to watch for changes to the parent directory and then check the file each time that directory changes. Good idea. I will try this later. > Also, why do you care about this value? This presence and format of this file isn't really considered API, so hard-coding that into an product that you ship to a wide variety of users would not be wise. Perhaps there's a better approach? Right now this is a private tool for my own amusement. Kind regards, Gerriet. P.S. I forgot to mention: this is 10.10. _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-kernel mailing list (Darwin-kernel(a)lists.apple.com) Help/Unsubscribe/Update your Subscription: https://lists.apple.com/mailman/options/darwin-kernel/site_archiver%40lists… This email sent to site_archiver(a)lists.apple.com

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Re: file changes content but ContentModificationDate not changing
by Quinn "The Eskimo!" 05 Nov '14

05 Nov '14

On 5 Nov 2014, at 13:13, Gerriet M. Denkmann <gerriet(a)mdenkmann.de> wrote: > Any way to observe changes (except from polling, which I am trying to avoid)? AFAICT ntpd doesn't write to this file, but rather writes to a temporary file and then replaces the original file with a temporary (using <x-man-page://2/rename>). This is a pretty typical 'safe save' technique. See save_drift_file in the following. <http://www.opensource.apple.com/source/ntp/ntp-92/ntpd/ntp_util.c> You can confirm this by checking the inode number of the file over time. $ ls -li /var/db/ntp.drift 9615173 -rw-r--r-- 1 root wheel 9 4 Nov 09:46 /var/db/ntp.drift It should change each time the file is saved. If this is, indeed, how things work, you'll have to watch for changes to the parent directory and then check the file each time that directory changes. * * * Also, why do you care about this value? This presence and format of this file isn't really considered API, so hard-coding that into an product that you ship to a wide variety of users would not be wise. Perhaps there's a better approach? Share and Enjoy -- Quinn "The Eskimo!" <http://www.apple.com/developer/> Apple Developer Relations, Developer Technical Support, Core OS/Hardware _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-kernel mailing list (Darwin-kernel(a)lists.apple.com) Help/Unsubscribe/Update your Subscription: https://lists.apple.com/mailman/options/darwin-kernel/site_archiver%40lists… This email sent to site_archiver(a)lists.apple.com

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file changes content but ContentModificationDate not changing
by Gerriet M. Denkmann 05 Nov '14

05 Nov '14

I am trying to observe changes of a file using dispatch_source_create(DISPATCH_SOURCE_TYPE_VNODE). But it does not work. The problem: the observed file (/var/db/ntp.drift) gets updated (about every hour) by a root-process (ntpd), Although the content of the file changes (I can open it in TextEdit and see changed values) the ContentModificationDate or AttributeModificationDate does often not change for days. Is this allowed to happen? Or a bug? Any way to observe changes (except from polling, which I am trying to avoid)? Gerriet. _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-kernel mailing list (Darwin-kernel(a)lists.apple.com) Help/Unsubscribe/Update your Subscription: https://lists.apple.com/mailman/options/darwin-kernel/site_archiver%40lists… This email sent to site_archiver(a)lists.apple.com

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Re: Timing / Scheduling issues / screensaver
by Jean Suisse 04 Nov '14

04 Nov '14

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Re: Timing / Scheduling issues / screensaver
by Jean Suisse 04 Nov '14

04 Nov '14

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Re: Timing / Scheduling issues / screensaver
by Shantonu Sen 04 Nov '14

04 Nov '14

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