Update to latest git, drop merged #686 patch
Adam Williamson
8 years ago
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From 93bda02b786f73acc8c109aa7f1616872980b735 Mon Sep 17 00:00:00 2001
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From: Adam Williamson <awilliam@redhat.com>
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Date: Wed, 4 Jan 2017 09:46:28 -0800
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Subject: [PATCH] Use `flock` not `fcntl` locking for portability (POO #13822)
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The structure used by `fcntl` to define the type, location, and
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length of the desired lock uses integer types - `off_t` and
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`pid_t` - that are platform dependent. When writing C you can
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just create a structure using those types, but when writing perl,
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there doesn't seem to be any terribly easy way to find out what
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`off_t` and `pid_t` actually are, in `pack()` terms. There's a
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fairly good discussion here:
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https://www.perlmonks.org/bare/index.pl?node_id=920008
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The code we currently have will work only on platforms where
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`off_t` happens to be a signed quad and `pid_t` happens to be
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a signed long. This seems to be the case for Fedora and SUSE
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64-bit arches, but certainly isn't the case for Fedora 32-bit
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arches (where `off_t` is a signed long instead), and it may
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differ in other scenarios too.
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So I suggest we just use perl `flock` to lock the file before
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writing instead. I've looked into it quite a lot, and AFAICS,
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none of the differences between `fcntl` and `flock` should be a
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problem for us. I don't think `vars.json` is ever likely to be
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on an NFS share (`flock` doesn't work over NFS), we don't need
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to lock a specific area of the file, and the fact that flock is
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an advisory file descriptor lock rather than a filesystem lock
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record should not be a problem, as AFAICS, this is the *only*
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code we ever use to write to `vars.json`, and it will certainly
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respect its own lock.
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---
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bmwqemu.pm | 3 ++-
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1 file changed, 2 insertions(+), 1 deletion(-)
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diff --git a/bmwqemu.pm b/bmwqemu.pm
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index 4f12b30..e07b5ae 100755
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--- a/bmwqemu.pm
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+++ b/bmwqemu.pm
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@@ -19,6 +19,7 @@ use strict;
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use warnings;
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use Time::HiRes qw(sleep gettimeofday);
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use IO::Socket;
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+use Fcntl ':flock';
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use Thread::Queue;
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use POSIX;
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@@ -80,7 +81,7 @@ sub save_vars() {
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my $fn = "vars.json";
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unlink "vars.json" if -e "vars.json";
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open(my $fd, ">", $fn);
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- fcntl($fd, F_SETLKW, pack('ssqql', F_WRLCK, 0, 0, 0, $$)) or die "cannot lock vars.json: $!\n";
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+ flock($fd, LOCK_EX) or die "cannot lock vars.json: $!\n";
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truncate($fd, 0) or die "cannot truncate vars.json: $!\n";
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# make sure the JSON is sorted
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@ -1 +1 @@
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SHA512 (os-autoinst-26171f41d6cab38e8707f2109663cb14e82a8e9a.tar.gz) = 42be0bd2dc60f2e61b1408c3889a65793349baa9ae8bb9b32e21df9c50c6c8c778e20ecc721ebd9afdb80a798908438262ea7f3206274f41537859f0c36d5911
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SHA512 (os-autoinst-84d91e68eb2d54f4967ccedb56f85a332ffbcbf3.tar.gz) = 3bc5de67678cc6a071097bd0d0805e335eac2e8d88684b5a89d16b967a7f59a43221d0acdb72b361091bdd78512bf799395081f481a90bb65dab685bace0d89d
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