Add some posix functions

[rosslagerwall]

BPO	10812
Nosy	@loewis, @birkenfeld, @gpshead, @ronaldoussoren, @abalkin, @pitrou, @giampaolo, @ned-deily
Files	mpos.patch: Patch + test for issue 10812_v2.patch: Updated patch 10812_v3.patch: Updated patch 10812_v4.patch: Updated patch, added sethostid, gethostname 10812_v5.patch: Updated patch, removed get/sethostname 10812_v6.patch: Fixes for OS X 10812_v7.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 = None
closed_at = <Date 2011-03-17.18:24:48.122>
created_at = <Date 2011-01-03.12:45:50.277>
labels = ['extension-modules', 'type-feature']
title = 'Add some posix functions'
updated_at = <Date 2012-07-31.17:55:28.929>
user = 'https://bugs.python.org/rosslagerwall'

bugs.python.org fields:

activity = <Date 2012-07-31.17:55:28.929>
actor = 'ronaldoussoren'
assignee = 'rosslagerwall'
closed = True
closed_date = <Date 2011-03-17.18:24:48.122>
closer = 'rosslagerwall'
components = ['Extension Modules']
creation = <Date 2011-01-03.12:45:50.277>
creator = 'rosslagerwall'
dependencies = []
files = ['20239', '20273', '20292', '20305', '20311', '20461', '21250']
hgrepos = []
issue_num = 10812
keywords = ['patch']
message_count = 26.0
messages = ['125162', '125174', '125183', '125187', '125414', '125454', '125555', '125604', '125634', '125690', '125729', '125730', '125749', '126598', '131088', '131090', '131111', '131168', '131169', '131275', '131282', '131398', '167012', '167015', '167016', '167021']
nosy_count = 11.0
nosy_names = ['loewis', 'georg.brandl', 'gregory.p.smith', 'ronaldoussoren', 'belopolsky', 'pitrou', 'giampaolo.rodola', 'ned.deily', 'Arfrever', 'rosslagerwall', 'python-dev']
pr_nums = []
priority = 'normal'
resolution = 'accepted'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue10812'
versions = ['Python 3.3']

[rosslagerwall]

Here's a patch that adds a bunch of posix functions that are missing from the posix module. Includes tests & documentation.

Tested on Linux & FreeBSD.

Specifically:
futimes
lutimes
futimens
fexecve
gethostid
sethostname
waitid
lockf
readv
pread
writev
pwrite
truncate
posix_fallocate
posix_fadvise
sync

[pitrou]

First couple comments:

• you don't have to modify Misc/NEWS yourself; it will probably make patch maintenance easier
• it would seem more natural for readv() to take a sequence of writable buffers (such as bytearrays) instead; I don't think the current signature is very useful
• readv() and writev() should support both lists and tuples, at the minimum (perhaps arbitrary iterables if you like to spend more time on it :-)): see the PySequence* API

[pitrou]

For the record, I get the following failures under OpenSolaris:

======================================================================
ERROR: test_lutimes (test.test_posix.PosixTester)
----------------------------------------------------------------------

Traceback (most recent call last):
 File "/home/antoine/py3k/cc/Lib/test/test_posix.py", line 265, in test_lutimes
 posix.lutimes(support.TESTFN, None)
AttributeError: 'module' object has no attribute 'lutimes'

======================================================================
ERROR: test_posix_fallocate (test.test_posix.PosixTester)
----------------------------------------------------------------------

Traceback (most recent call last):
 File "/home/antoine/py3k/cc/Lib/test/test_posix.py", line 236, in test_posix_fallocate
 posix.posix_fallocate(fd, 0, 10)
OSError: [Errno 22] Invalid argument

[pitrou]

According to the posix_fallocate() man page under OpenSolaris:

 EINVAL The len argument is less than or equal to zero, or
 the offset argument is less than zero, or the
 underlying file system does not support this
 operation.

I would go for the third (last) interpretation: the filesystem (ZFS here) doesn't support it.

[rosslagerwall]

This patch:

Fixes test_lutimes(),
Ignores a posix_fallocate() failure on Solaris due to ZFS,
Changes readv() & writev() signatures such that they take sequences instead of tuples,
Changes readv() so that it takes a number of writable buffers, fills them and returns the total number of bytes read.

[abalkin]

The patch contains a lot of repeated boilerplate code. I wonder if some of it can be factored out and reused. For example iov buffer allocation code appears to be identical in writev and readv.

[rosslagerwall]

This new patch reuses iov allocation code between readv & writev.
It reuses code between exec, execve & fexecve.
It reuses code for parsing off_t types.

I've tried where possible to reuse code but I think though that the code seems pretty standard for the posix module. Each function pretty much parses args, calls posix function, checks for error and returns result.

[loewis]

Patch looks mostly good. Some comments:

• sethostname supports names with embedded null bytes, so
  wrapper should not use strlen
• it's a bit asymmetric that gethostname is in the socket
  module and supports Windows, and sethostname is in the POSIX
  module. It would be useful to have a gethostname in the POSIX
  module also which is a) POSIX only and b) supports embedded
  NUL bytes.
• I think get/sethostname should use the FSDefault encoding.
• gethostid should check for POSIX errors.
• it checks for sethostid but then doesn't implement it.
• parsing id_t with "l" is incorrect, methinks
• siginfo_t should map to a structsequence
• according to my copy of waitid(2), not all of the fields you
  are returning from siginfo_t are actually filled.
• instead of PARSE_OFF_T, I rather recommend to use an O& parser.

[rosslagerwall]

it's a bit asymmetric that gethostname is in the socket
module and supports Windows, and sethostname is in the POSIX
module. It would be useful to have a gethostname in the POSIX
module also which is a) POSIX only and b) supports embedded
NUL bytes.

According to the spec for gethostname(), the hostname that it returns is null-terminated so it won't support embedded NUL bytes. Should we still add it anyway?

[rosslagerwall]

Thanks for the comments.

I implemented sethostid() - its not actually in the posix spec, but linux/*bsd
have it although the signature for FreeBSD is a bit different.

I implemented gethostname(). Both get/sethostname() now use FSDefault encoding.
gethostname() is null-terminated so it doesn't have to deal with embedded NULs.
sethostname() works with embedded NULs.

Since id_t can contain a pid_t, I now parse id_t with _Py_PARSE_PID.
waitid() also now returns a structsequence of the correct fields.

According to the spec, gethostid does not set errno - it now checks anyway.

Instead of PARSE_OFF_T, I use a O& parser.

[loewis]

According to the spec for gethostname(), the hostname that it returns
is null-terminated so it won't support embedded NUL bytes. Should we
still add it anyway?

Oops, I misread the spec. No, gethostname should then not be duplicated.
Putting sethostname into the socket module might be worth considering,
though; I find the proposed split confusing.

[loewis]

According to the spec, gethostid does not set errno - it now checks anyway.

Sorry, I misread that also. Leaving the check is fine; reverting it to
the previous code would be fine as well.

[rosslagerwall]

This patch takes out sethostname() and gethostname(). I'll open up a new issue to add sethostname() to the socket module.