sendfile implementation is not compatible with Solaris

[kulikjak]

BPO	41687
Nosy	@ambv, @1st1, @miss-islington, @isidentical, @kulikjak
PRs	bpo-41687: Fix sendfile implementation to work with Solaris #22040 bpo-41687: Fix error handling in Solaris sendfile implementation #22128 [3.9] bpo-41687: Fix sendfile implementation to work with Solaris (GH-22040) #22273 [3.9] bpo-41687: Fix error handling in Solaris sendfile implementation (GH-22128) #22274

^{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 2020-09-05.19:10:31.396>
created_at = <Date 2020-09-01.13:55:22.051>
labels = ['3.8', 'type-bug', 'library', '3.9', '3.10']
title = 'sendfile implementation is not compatible with Solaris'
updated_at = <Date 2020-09-16.12:25:16.758>
user = 'https://github.com/kulikjak'

bugs.python.org fields:

activity = <Date 2020-09-16.12:25:16.758>
actor = 'miss-islington'
assignee = 'none'
closed = True
closed_date = <Date 2020-09-05.19:10:31.396>
closer = 'yselivanov'
components = ['Library (Lib)']
creation = <Date 2020-09-01.13:55:22.051>
creator = 'kulikjak'
dependencies = []
files = []
hgrepos = []
issue_num = 41687
keywords = ['patch']
message_count = 6.0
messages = ['376191', '376439', '376475', '376658', '376988', '376990']
nosy_count = 5.0
nosy_names = ['lukasz.langa', 'yselivanov', 'miss-islington', 'BTaskaya', 'kulikjak']
pr_nums = ['22040', '22128', '22273', '22274']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue41687'
versions = ['Python 3.8', 'Python 3.9', 'Python 3.10']

[kulikjak]

Hi,

Sendfile on Solaris raises EINVAL if offset is equal or bigger than the size of the file. This is different from Linux, where similar sendfile call returns 0, which is used in an ad-hoc fashion to indicate EOF. Since Python sendfile implementation expects 0 to be returned, it breaks. I already reported this in bpo-36610, which led to sendfile eventually being disabled on Solaris to be safe before the 3.8 release.

We were first looking into a possibility to change Solaris behavior of sendfile to reflect that of Linux but decided not to because of the significant risk that it can break existing programs. The other reason is that sendfile isn't standardized (Linux manpage explicitly states that) and hence Solaris implementation isn't broken, just different. Because of that, we patched the runtime and added #ifdef branch (of which there are already many due to os differences) with additional offset check. It is tested with the current master and also 3.7, which we are using internally.

Thanks

[1st1]

New changeset 8c0be6f by Jakub Kulík in branch 'master':
bpo-41687: Fix sendfile implementation to work with Solaris (bpo-22040)
8c0be6f

[kulikjak]

I just realized that the recently merged PR has broken error handling, so I opened another one with a followup fix.

[miss-islington]

New changeset fa8c9e7 by Jakub Kulík in branch 'master':
bpo-41687: Fix error handling in Solaris sendfile implementation (GH-22128)
fa8c9e7

[ambv]

New changeset 7e356f1 by Łukasz Langa in branch '3.9':
[3.9] bpo-41687: Fix sendfile implementation to work with Solaris (GH-22040) (GH-22273)
7e356f1

[miss-islington]

New changeset 6a39888 by Miss Islington (bot) in branch '3.9':
bpo-41687: Fix error handling in Solaris sendfile implementation (GH-22128)
6a39888