Bug #128340 for Sys-PageCache: suggest no file length check

Wed Jan 23 20:06:13 2019 user42_kevin [...] yahoo.com.au - Ticket created

Subject:	suggest no file length check
Date:	Thu, 24 Jan 2019 11:59:41 +1100
To:	bug-Sys-PageCache [...] rt.cpan.org
From:	Kevin Ryde <user42_kevin [...] yahoo.com.au>

I see fadvise() checks the length of the file and warns if the advised region exceeds the length. As a suggestion, I think that could be omitted. I think the system call allows regions beyond the end of a file and quietly ignores the excess. If a file size is changing, or if you're just advising about say the next 10 kbytes from current file position which you're going to read, then it'd be convenient not to worry about possibly being past the end.

Wed Jan 23 23:40:41 2019 hirose31 [...] gmail.com - Correspondence added

On 2019-1月-23 水 20:06:13, user42_kevin@yahoo.com.au wrote: Show quoted text

> I think the system call allows regions beyond the end of a file and > quietly ignores the excess. If a file size is changing, or if you're

Is this documented behavior? I cannot find in this document: http://man7.org/linux/man-pages/man2/posix_fadvise.2.html I think it is not good relying on undocumented behavior.

Wed Jan 23 23:40:42 2019 The RT System itself - Status changed from 'new' to 'open'

Fri Jan 25 17:57:09 2019 user42_kevin [...] yahoo.com.au - Correspondence added

Subject:	Re: [rt.cpan.org #128340] suggest no file length check
Date:	Sat, 26 Jan 2019 09:50:10 +1100
To:	"HIROSE Masaaki via RT" <bug-Sys-PageCache [...] rt.cpan.org>
From:	Kevin Ryde <user42_kevin [...] yahoo.com.au>

"HIROSE Masaaki via RT" <bug-Sys-PageCache@rt.cpan.org> writes: Show quoted text

> > Is this documented behavior? > http://man7.org/linux/man-pages/man2/posix_fadvise.2.html

I think so, where it says The advice applies to a (not necessarily existent) region so the region doesn't have to exist. Show quoted text

> I think it is not good relying on undocumented behavior.

I'd suggest just making the system call(s), since the system will say an errno etc if it doesn't like what you do.

Sun Jan 27 23:38:56 2019 hirose31 [...] gmail.com - Correspondence added

Hi, Could you send a pull request? https://github.com/hirose31/Sys-PageCache/pulls