linux-ext4 - Re: [RFC] Optimizing readdir()

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Message-ID: <87wqvge1nt.fsf@flamingspork.com>
Date:	Mon, 14 Jan 2013 17:09:26 +1100
From:	Stewart Smith <stewart@...mingspork.com>
To:	Theodore Ts'o <tytso@....edu>, Radek Pazdera <rpazdera@...hat.com>
Cc:	linux-ext4@...r.kernel.org,
	Lukáš Czerner <lczerner@...hat.com>
Subject: Re: [RFC] Optimizing readdir()

Theodore Ts'o <tytso@....edu> writes:
> I wonder if the better approach is to just simply have some
> easy-to-use library routines that do a readdir/sort in userspace.  The
> spd_readdir does basically this, and as we can see it's good enough
> for most purposes.  The problem is danger when using this in threaded
> programs, or if you have programs doing really strange things with
> telldir/seekdir, etc.
>
> But it wouldn't be that hard to write a generic library function which
> if it were used for find, ls, tar, and a few other key programs, would
> solve the problem for most use cases.

Many times I've used scandir(3) to do this.

(copying out of notmuch/notmuch-new.c):

static int
dirent_sort_inode (const struct dirent **a, const struct dirent **b)
{
    return ((*a)->d_ino < (*b)->d_ino) ? -1 : 1;
}

(as then doing stat() on each file is *much* faster in inode order)

glibc provides alphasort() (POSIX.1-2008) and versionsort() (GNU
extension), it'd probably be great if it also provided inodesort()

-- 
Stewart Smith

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