thestig@, we'll need this fixed for M51.  Will you be around to take a look in the next couple weeks?

This is a silly question, but why are you watching /system at all? Those files never change.

It's an artifact of the way our abstraction on inotify, FilePathWatcher, works. It appears to add an inotify watch on each subpath leading to the leaf file. In #11 above, the list of inotify_add_watch show this happening (/system/etc/hosts gets watchers for each parent, grandparent, grand-grandparent, etc.). The code that does this is the second link in the #18, which was added by the third link in #18.

Also, I should correct #18: it's not actually using recursive inotify; it's just building up inotify watchers for each sub-path element.

Even before I implemented recursive FilePathWatcher for Linux, FilePathWatcher had its current behavior of splitting up a watched path to its components and adding watches for each component.

nnk@ says /system never changes, so it seems the issue here is why Chromium bothers to add the watch at all. It looks like r246101 added the code that calls into FilePathWatcher, so punting this to that CL's author.

Is this a regression or something discovered recently?

I haven't confirmed myself, but there are articles talking about modifying /system/etc/hosts on rooted devices. It's probably OK for us to remove the FilePathWatcher in that case.

However - wouldn't any recursive FilePathWatcher end up trying to watch / and running into the same problem? Happy to move that to a separate bug.

I think this is a new restriction in N. I agree there are two issues here, 1) if /system/etc/hosts doesn't change, there's no point in watching it; 2) other users of FilePathWatcher will trigger this issue as well.

AFAICT, there's no other uses of FilePathWatcher::Watch() on Android. The only other Android use in my week old checkout is from component/drive/ and that was recently removed in r384242.

OK. julia, can you remove the use of this soon? Thanks

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/a2e7ea61ce75af85c4479c5af292383e3cf08341

commit a2e7ea61ce75af85c4479c5af292383e3cf08341
Author: juliatuttle <juliatuttle@chromium.org>
Date: Thu May 05 13:56:36 2016

Async DNS: Don't watch hosts file on Android

The hosts file on Android should never change (it's on the read-only
/system partition), and attempting to watch it also tries to watch /,
which triggers a SELinux denial in Android N.

Therefore, don't watch it on Android.

BUG= 600442 

Review-Url: https://codereview.chromium.org/1906573002
Cr-Commit-Position: refs/heads/master@{#391799}

[modify] https://crrev.com/a2e7ea61ce75af85c4479c5af292383e3cf08341/net/dns/dns_config_service_posix.cc
[modify] https://crrev.com/a2e7ea61ce75af85c4479c5af292383e3cf08341/net/dns/dns_config_service_posix_unittest.cc

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The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/8118cdeafceca82dcff6e180ea9b35f674563fb7

commit 8118cdeafceca82dcff6e180ea9b35f674563fb7
Author: Julia Tuttle <juliatuttle@chromium.org>
Date: Tue May 10 17:42:39 2016

Async DNS: Don't watch hosts file on Android

The hosts file on Android should never change (it's on the read-only
/system partition), and attempting to watch it also tries to watch /,
which triggers a SELinux denial in Android N.

Therefore, don't watch it on Android.

BUG= 600442 

Review-Url: https://codereview.chromium.org/1906573002
Cr-Commit-Position: refs/heads/master@{#391799}
(cherry picked from commit a2e7ea61ce75af85c4479c5af292383e3cf08341)

Review URL: https://codereview.chromium.org/1965553005 .

Cr-Commit-Position: refs/branch-heads/2704@{#478}
Cr-Branched-From: 6e53600def8f60d8c632fadc70d7c1939ccea347-refs/heads/master@{#386251}

[modify] https://crrev.com/8118cdeafceca82dcff6e180ea9b35f674563fb7/net/dns/dns_config_service_posix.cc
[modify] https://crrev.com/8118cdeafceca82dcff6e180ea9b35f674563fb7/net/dns/dns_config_service_posix_unittest.cc