Add open_file_descriptor parameter to fcntl.lockf() (use the new F_OFD_SETLK flag)

[AndrewLutomirski]

BPO	22367
Nosy	@pitrou, @vstinner, @ned-deily, @ambv, @serhiy-storchaka, @hvenev, @aixtools, @corona10, @miss-islington, @iforapsy
PRs	bpo-22367: Add test_lockf #17010 [3.8] bpo-22367: Add tests for fcntl.lockf(). (GH-17010) #17084 [3.7] bpo-22367: Add tests for fcntl.lockf(). (GH-17010) #17085 bpo-22367: Add open_file_descriptor parameter to fcntl.lockf() #17099 bpo-22367: Update test_fcntl.py for spawn process mode #17154 [3.8] bpo-22367: Update test_fcntl.py for spawn process mode (GH-17154) #17252 [3.7] bpo-22367: Update test_fcntl.py for spawn process mode (GH-17154) #17253
Files	0001-fcntl-support-F_OFD_.patch 0002-fcntl-Support-Linux-open-file-descriptor-locks.patch

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = 'https://github.com/corona10'
closed_at = None
created_at = <Date 2014-09-08.20:18:49.508>
labels = ['type-feature', 'library', '3.9']
title = 'Add open_file_descriptor parameter to fcntl.lockf() (use the new F_OFD_SETLK flag)'
updated_at = <Date 2019-12-07.20:10:28.686>
user = 'https://bugs.python.org/AndrewLutomirski'

bugs.python.org fields:

activity = <Date 2019-12-07.20:10:28.686>
actor = 'ned.deily'
assignee = 'corona10'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2014-09-08.20:18:49.508>
creator = 'Andrew.Lutomirski'
dependencies = []
files = ['42085', '42093']
hgrepos = []
issue_num = 22367
keywords = ['patch']
message_count = 34.0
messages = ['226610', '261295', '261310', '261353', '261354', '261365', '355512', '355522', '356212', '356295', '356296', '356328', '356329', '356607', '356614', '356675', '356678', '356681', '356815', '356816', '356837', '356849', '356852', '356913', '356938', '356952', '356954', '357251', '357253', '357255', '357264', '357286', '357287', '357984']
nosy_count = 11.0
nosy_names = ['pitrou', 'vstinner', 'ned.deily', 'lukasz.langa', 'serhiy.storchaka', 'Andrew.Lutomirski', 'h.venev', 'Michael.Felt', 'corona10', 'miss-islington', 'iforapsy']
pr_nums = ['17010', '17084', '17085', '17099', '17154', '17252', '17253']
priority = None
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue22367'
versions = ['Python 3.9']

[AndrewLutomirski]

Linux 3.15 and newer support a vastly superior API for file locking, in which locks are owned by open file descriptions instead of by processes. This is how everyone seems to expect POSIX locks to work, but now they can finally work that way.

Please add some interface to these locks to fcntl.lockf. One option would be to use them by default and to fall back to standard POSIX locks if they're not available. I don't know whether this would break existing code.

See http://man7.org/linux/man-pages/man2/fcntl.2.html for details.

[hvenev]

I'd like to use fd locks from python too.

[hvenev]

This implements the open_file_descriptor argument and fixes a bug with converting to int when off_t is 64-bit but long is 32-bit.

[vstinner]

This implements the open_file_descriptor argument and fixes a bug with converting to int when off_t is 64-bit but long is 32-bit.

Please extract the fix into a different patch.

[vstinner]

Strange, Rietveld (the tool linked with the [review] button) doesn't show the change on the Modules/fcntlmodule.c file.

By the way, I suggest to not include the Modules/clinic/fcntlmodule.c.h change in the patch.

[hvenev]

Here is the OFD patch, I'll open another issue for the overflow bug.

[corona10]

On bpo-38602, the constant related to open file descriptors will be added.
I will finalize this issue after bpo-38602 is closed.

[vstinner]

On bpo-38602, the constant related to open file descriptors will be added. I will finalize this issue after bpo-38602 is closed.

bpo-38602 added constants, but this issue also modify lockf() to add open_file_descriptor parameter to choose between F_SETLK/F_SETLKW and F_OFD_SETLK/F_OFD_SETLKW.

[serhiy-storchaka]

New changeset befa032 by Serhiy Storchaka (Dong-hee Na) in branch 'master':
bpo-22367: Add tests for fcntl.lockf(). (GH-17010)
befa032

[miss-islington]

New changeset 85e4151 by Miss Islington (bot) in branch '3.8':
bpo-22367: Add tests for fcntl.lockf(). (GH-17010)
85e4151