Different users on the same mapset

[Seppo Kaitala]

Hi Luca 

Maybe too trivial, but if you put the data in mapset PERMANENT,
different users can access the data.

Seppo Kaitala

Luca Palmeri wrote:
> 
> Dear grass comunity,
> 
>         Yesterday for the first time since I use grass, I have been
> 
> faced with an interesting question:
> 
>         can different users work on the same mapset ?
> 
> So I tried, I played with unix privileges moved mapsets changed user
> 
> and group etc. etc. and discovered that finally THE ANSWER IS NO !!!
> 
> at lest not in grass5beta3 on alinux RH6.0 (posix compliant) platform.
> 
> Well, this is a little bit strange. Why shouldn't be possible in a
> 
> multi user environment such as unix to use the same mapset under
> 
> different usernames (maybe in the same group) ?
> 
> This could be very usefull especially for large projects whit many
> 
> people involved in.
> 
> The problem is in a GRASS GIS library call G__mapset_permissions,
> 
> that looks like:
> 
> int G__mapset_permissions (char *mapset)
> {
>     char path[256];
>     struct stat info;
> 
>     G__file_name (path,"","",mapset);
> 
>     if (stat (path, &info) != 0)
>             return -1;
> 
>     if (info.st_uid != getuid())
>             return 0;
>     if (info.st_uid != geteuid())
>             return 0;
> 
>     return 1;
> }
> 
> Simple, everytime that a call access mapsets data a check is done
> 
> for the userid of the mapsets file to be equal to that of real and
> 
> effective ids of the invoking process. So if I own a mapset I can
> 
> work on it, if I do not own it I cannot regardeless of the unix
> 
> mapsets files privileges.
> 
> I have only one question, why ? I do not understand this idea.
> 
> Ok so I went forward and changed a little bit the code. But if we
> 
> release this constraint by for example commenting the last two ifs
> 
> in the call, we will have to check for access permission to the mapsets.
> 
> This is done at start time in gis_set. I've done some work on that
> 
> and modified the gis_set and the g.access programs.
> 
> Anyhow at this stage I do not think it is a good idea to post my bugfixes,
> 
> that are to be considered much more as tournarounds. A sound understanding
> 
> of the global grass structure and clear objectives on how to manage mapset
> 
> permissions are needed in order to produce a proper code.
> 
> So here I just want to point out that THIS IS AN IMPORTANT ISSUE. Clearly
> 
> if somebody is interested in having my patch I can send it. But I would first
> 
> like to understand the developping strategy beneath the G__mapset_permissions
> 
> call.
> 
> Comments are welcome
> 
> LP
> 
> --> Luca Palmeri - Dip. Proc. Chimici dell'Ingengeria
>     Universita' di Padova  TEL: +390498275527 -------
> -------------------------  FAX: +390498275528 -------
> --> Think holistic @ the end of the 2nd millenium <--
> 
>