Avoid unnecessary file churn by "git reset --hard" step.

Avoid unnecessary file churn by "git reset --hard" step.

Some of the build step create hard-links to files in the checked out
repository which change the file ctime timestamp even. In turn, this
cause "git reset --hard" to consider the file as modified due to a
cache mismatch between its index and the checkout.

As a workaround, add a "git update-index --refresh" call to force a
refresh of the git index, which will update the ctime stored in the
cache, thus avoiding the unnecessary recreation of the file. This is
necessary as otherwise ninja would consider the output of the
hardlink step as stale and would re-run the corresponding step
thus creating a vicious cycle.

BUG=642711
Committed: https://chromium.googlesource.com/chromium/tools/build/+/a3067d9bb46a84753a2c19dd391b9896c629dfbf

[sdefresne, 2016-10-26 14:56:24]

The CQ bit was checked by sdefresne@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2016-10-26 14:56:30]

Dry run: CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2016-10-26 14:56:31]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2016-10-26 14:56:32]

Dry run: No L-G-T-M from a valid reviewer yet. 
CQ run can only be started by full committers or once the patch has
received an L-G-T-M from a full committer.
Even if an L-G-T-M may have been provided, it was from a non-committer,
_not_ a full super star committer.
Committers are members of the group "project-infra-committers".
Note that this has nothing to do with OWNERS files.

[sdefresne, 2016-10-26 14:56:56]

sdefresne@chromium.org changed reviewers:
+ dpranke@chromium.org, justincohen@chromium.org

[sdefresne, 2016-10-26 14:56:57]

justincohen: FYI
dpranke: Please take a look.

[justincohen, 2016-10-26 15:53:33]

lgtm, can you update the Cl description with the --refresh flag

[sdefresne, 2016-10-26 15:56:53]

Description was changed from

==========
Avoid unnecessary file churn by "git reset --hard" step.

Some of the build step create hard-links to files in the checked out
repository which change the file ctime timestamp even. In turn, this
cause "git reset --hard" to consider the file as modified due to a
cache mismatch between its index and the checkout.

As a workaround, add a "git update-index" call to force a refresh of
the git index, which will update the ctime stored in the cache, thus
avoiding the unnecessary recreation of the file. This is necessary as
otherwise ninja would consider the output of the hardlink step as
stale and would re-run the corresponding step thus creating a vicious
cycle.

BUG=642711
==========

to

==========
Avoid unnecessary file churn by "git reset --hard" step.

Some of the build step create hard-links to files in the checked out
repository which change the file ctime timestamp even. In turn, this
cause "git reset --hard" to consider the file as modified due to a
cache mismatch between its index and the checkout.

As a workaround, add a "git update-index --refresh" call to force a
refresh of the git index, which will update the ctime stored in the
cache, thus avoiding the unnecessary recreation of the file. This is
necessary as otherwise ninja would consider the output of the
hardlink step as stale and would re-run the corresponding step
thus creating a vicious cycle.

BUG=642711
==========

[sdefresne, 2016-10-26 15:57:01]

On 2016/10/26 15:53:33, justincohen wrote:
> lgtm, can you update the Cl description with the --refresh flag

Done.

[Dirk Pranke, 2016-10-26 17:26:04]

lgtm

[sdefresne, 2016-10-26 17:36:11]

The CQ bit was checked by sdefresne@chromium.org

[commit-bot: I haz the power, 2016-10-26 17:36:17]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2016-10-26 17:45:53]

Description was changed from

==========
Avoid unnecessary file churn by "git reset --hard" step.

Some of the build step create hard-links to files in the checked out
repository which change the file ctime timestamp even. In turn, this
cause "git reset --hard" to consider the file as modified due to a
cache mismatch between its index and the checkout.

As a workaround, add a "git update-index --refresh" call to force a
refresh of the git index, which will update the ctime stored in the
cache, thus avoiding the unnecessary recreation of the file. This is
necessary as otherwise ninja would consider the output of the
hardlink step as stale and would re-run the corresponding step
thus creating a vicious cycle.

BUG=642711
==========

to

==========
Avoid unnecessary file churn by "git reset --hard" step.

Some of the build step create hard-links to files in the checked out
repository which change the file ctime timestamp even. In turn, this
cause "git reset --hard" to consider the file as modified due to a
cache mismatch between its index and the checkout.

As a workaround, add a "git update-index --refresh" call to force a
refresh of the git index, which will update the ctime stored in the
cache, thus avoiding the unnecessary recreation of the file. This is
necessary as otherwise ninja would consider the output of the
hardlink step as stale and would re-run the corresponding step
thus creating a vicious cycle.

BUG=642711

Committed:
https://chromium.googlesource.com/chromium/tools/build/+/a3067d9bb46a84753a2c...
==========

[commit-bot: I haz the power, 2016-10-26 17:45:54]

Committed patchset #1 (id:1) as
https://chromium.googlesource.com/chromium/tools/build/+/a3067d9bb46a84753a2c...