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Re: creating backups in temporary directories

From: David Kastrup
Subject: Re: creating backups in temporary directories
Date: Mon, 10 Sep 2007 21:55:11 +0200
User-agent: Gnus/5.11 (Gnus v5.11) Emacs/22.1.50 (gnu/linux)

"Davis Herring" <address@hidden> writes:

>> Well, seems I misread the manual page for open/creat.  I thought that
>> without O_EXCL, the file would get replaced.
>> Well, then there still is the contorted way of hard linking /tmp/foo
>> to /tmp/foo~, opening /tmp/randomfilename for write, renaming it to
>> /tmp/foo and then finishing the write operation.
> Why not just rename /tmp/foo to /tmp/foo~, then open /tmp/foo with O_EXCL?
>  If it fails, then write (again with O_EXCL) to /tmp/randomfile so that
> the user's work is on disk -somewhere-, and tell them that they have
> enemies.

I would simply not save at all if O_EXCL fails, leave the buffer
marked as modified, and set a buffer-permanent local variable
save-only-when-nonexistent to buffer-filename.  Attempts to save the
buffer to a file with the filename save-only-when-nonexistent will use

Auto save files should always be opened O_EXCL.

When a file lock for a non-existing file is created,
save-only-when-nonexistent is set at the same time.  Hm, this is sort
of a mess.  There will always be somewhat predictable names on /tmp
and similar.  Perhaps we should have some rule not to write through
symlinks in such directories after all.

David Kastrup, Kriemhildstr. 15, 44793 Bochum

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