On Mon, Nov 4, 2013 at 3:48 PM, Richard Hughes <hughsient@xxxxxxxxx> wrote:
> On 4 November 2013 14:31, Miloslav Trmač <mitr@xxxxxxxx> wrote:
>> That's true in the _general_ case, and therefore the ability to have
>> off-line updates is a good _general_ default. We should be able to do
>> _much_ better for many common cases (at the very least, a package that
>> only has one executable, or one shared library, and no other
>> executables or shared libraries or data files with unknown function).
>
> Even that's basically impossible to do in a race-free way. The way rpm
> works is when you update a package, you actually install the new
> package, then remove the old one. So there's a small but significant
> time where just launching a command line utility makes it crash.
That's not what strace says:
> open("/usr/bin/youtube-dl;5277b6fc", O_WRONLY|O_CREAT|O_TRUNC, 0666) = 46
<snip>
> close(46) = 0
<snip>
> write(46, "#!/usr/bin/env python\nPK\3\4\24\0\0\0\10\0"..., 65536) = 65536
<snip>
> rename("/usr/bin/youtube-dl;5277b6fc", "/usr/bin/youtube-dl") = 0
rename() is atomic, so at every single moment the path refers to a
valid and working executable. (The heuristic above has been
intentionally worded in a way that avoids inter-file dependencies.)
Mirek
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