From: Mark Walters <markwalters1009@gmail.com>
To: Peter Wang <novalazy@gmail.com>
Subject: Re: [PATCH 05/18] insert: move file from Maildir tmp to new
In-Reply-To: <20121119232651.GB2063@hili.localdomain>
References: <1343223767-9812-1-git-send-email-novalazy@gmail.com>
	<1343223767-9812-5-git-send-email-novalazy@gmail.com>
	<87haomq0hx.fsf@qmul.ac.uk>
	<20121119232651.GB2063@hili.localdomain>
User-Agent: Notmuch/0.14+81~g9730584 (http://notmuchmail.org) Emacs/23.4.1
	(x86_64-pc-linux-gnu)
Date: Mon, 19 Nov 2012 13:49:05 +0000
Message-ID: <874nklpusu.fsf@qmul.ac.uk>
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Cc: notmuch@notmuchmail.org
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Hi 

On Mon, 19 Nov 2012, Peter Wang <novalazy@gmail.com> wrote:
> On Sun, 18 Nov 2012 17:33:46 +0000, Mark Walters <markwalters1009@gmail.com> wrote:
>> On Wed, 25 Jul 2012, Peter Wang <novalazy@gmail.com> wrote:
>> > Atomically move the new message file from the Maildir 'tmp' directory
>> > to 'new'.
>> > ---
>> >  notmuch-insert.c |   18 ++++++++++++++++++
>> >  1 files changed, 18 insertions(+), 0 deletions(-)
>> >
>> > diff --git a/notmuch-insert.c b/notmuch-insert.c
>> > index 340f7e4..bab1fed 100644
>> > --- a/notmuch-insert.c
>> > +++ b/notmuch-insert.c
>> > @@ -75,6 +75,20 @@ maildir_open_tmp (void *ctx, const char *dir, char **tmppath, char **newpath)
>> >  }
>> >  
>> >  static notmuch_bool_t
>> > +maildir_move_to_new (const char *tmppath, const char *newpath)
>> > +{
>> > +    /* We follow the Dovecot recommendation to simply use rename()
>> > +     * instead of link() and unlink().
>> > +     */
>> > +    if (rename (tmppath, newpath) == 0) {
>> > +	return TRUE;
>> > +    }
>> 
>> Do we want to overwrite an existing message with this name? As far as I
>> can see rename does overwrite and link would not: was that why rename is
>> better than link/unlink?
>> 
>> I would prefer not to overwrite but maybe there is a reason we need to. 
>> Would a possible alternative be to loop when finding a tmp file until
>> both the tmp file and the new file do not exist?
>
> According to [1] it's all pointless -- just generate unique file names.
>
> The dovecot maildir-save.c has this comment:
>
> /* maildir spec says we should use link() + unlink() here. however
>    since our filename is guaranteed to be unique, rename() works just
>    as well, except faster. even if the filename wasn't unique, the
>    problem could still happen if the file was already moved from
>    new/ to cur/, so link() doesn't really provide any safety anyway.
>
>    Besides the small temporary performance benefits, this rename() is
>    almost required with OSX's HFS+ filesystem, since it implements
>    hard links in a pretty ugly way, which makes the performance crawl
>    when a lot of hard links are used. */
>
> Well, that's one point of view.  I can't say I know any better.

I think I agree with you/them. Indeed, since files in cur can have
maildir flags we could find that this rename works but then the new file
gets stomped on by notmuch_message_tags_to_maildir_flags which also uses
rename. It might be work adding the link to [1] in the comment, but in
any case I am happy with this now.

Best wishes

Mark

>
> Peter
>
> [1]: http://wiki.dovecot.org/MailboxFormat/Maildir#Mail_delivery