linux-kernel - Re: [rfc] new stat*fs-like syscall?

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Date:	Tue, 06 Jul 2010 08:31:30 +0900
From:	"J. R. Okajima" <hooanon05@...oo.co.jp>
To:	Brad Boyer <flar@...andria.com>
Cc:	Christoph Hellwig <hch@...radead.org>,
	Nick Piggin <npiggin@...e.de>, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, Al Viro <viro@...IV.linux.org.uk>,
	Ulrich Drepper <drepper@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [rfc] new stat*fs-like syscall?


Brad Boyer:
> I would suggest making it an inode operation if we do actually add it. Most
> cases are going to be per super-block, but it might be easier to transparently
> handle things like _PC_PIPE_BUF in glibc if it could call an fpathconf type
> system call on the pipe fd. I haven't looked at the current glibc code for
> that particular selector. The only one I looked at in any detail was
> _PC_LINK_MAX, which is the one you already discussed and is obviously a
> per-sb option. The only drawback I can see is that making it an inode
> operation would make the vfs_pathconf fail on a negative dentry, but that
> seems like a very strange thing to support in any case.

Recently the size of the pipe buffer becomes customizable, doesn't it?
For _PC_PIPE_BUF, fpathconf should issue fcntl(F_GETPIPE_SZ).

For negative dentry, it should be supported as long as some
standard/specification doesn't prohibit explicitly. So I still think
statfs is the best place to implement _PC_LINK_MAX.


J. R. Okajima
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