[Dovecot] Running on HPUX

[Timo Sirainen]

On Fri, 2006-06-23 at 16:13 -0700, Rich Rauenzahn wrote:
> I think multiple mmap's of the same file are verboten --
> 
>          +  In most cases, two separate calls to mmap() cannot map
>               overlapping ranges in a file.  The virtual address range
>               reserved for a file range is determined at the time of the
>               initial mapping of the file range into a process address
>               space.  The system allocates only the virtual address range
>               necessary to represent the initial mapping.  As long as the
>               initial mapping exists, subsequent attempts to map a different
>               file range that includes any portion of the initial range may
>               fail with an ENOMEM error if an extended contiguous address
>               range that preserves the mappings of the initial range cannot
>               be allocated.

Well, I don't see anything like that described in Linux or UNIX98 man
pages..

> So, I was trying to look at why the index file is being mapped twice, 
> and why the addr isn't saved and reused.

The problem has something to do with how index file code works
internally. A "view" is (supposed to be) a snapshot of the mailbox at a
given state. It's not updated until the view is synchronized. Each view
points to a "map" which contains the index file's mmap pointer and other
information, including records_count which tells how many messages it
holds.

mail_index_map() is used to get the latest mapping of the index file. If
the existing latest map is already used by views, Dovecot simply
discards the existing map and mmap()s the file all over again.

One way to handle this would be to unmap the existing area always,
mmap() it and update all the existing maps' pointer to the new one. But
since the maps may have different files mmapped (the index file could
have been rebuilt and the maps point to different files), it's not that
simple to implement.

Another workaround would be to move the map to memory and let the views
use that. That would be pretty easy to implement, but if HP-UX is the
only OS where this breaks, I think I'll just leave it as it is since
it's faster this way..

Anyway, I think something like this should fix it (not tested):

diff -u -r1.230.2.5 mail-index.c
--- src/lib-index/mail-index.c  17 Jun 2006 13:42:36 -0000      1.230.2.5
+++ src/lib-index/mail-index.c  24 Jun 2006 19:35:30 -0000
@@ -1031,6 +1031,15 @@
                /* this map is already used by some views and they may have
                   pointers into it. leave them and create a new mapping. */
                if (!index->mmap_disable) {
+                       struct mail_index_map *old_map;
+
+                       old_map = index->map;
+                       map = mail_index_map_clone(index->map,
+                                                  index->map->hdr.record_size);
+                       map->refcount = index->map->refcount;
+                       mail_index_unmap(index, &index->map);
+                       *old_map = *map;
+                       i_free(map);
                        map = NULL;
                } else {
                        /* create a copy of the mapping instead so we don't

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