Hi Johannes, > perhaps it is a stupid question but I do not well understand > why HPLIP requires continuously running processes (i.e. daemons).
Currently hpiod is a persistent daemon in order to maintain 1284.4/MLC state for multiple clients/processes. 1284.4/MLC is a multi-point transport over a single endpoint. Over this transport multiple channels are supported for printing, scanning, status and faxing. With that said, we have learned a lot since we have started the HPLIP project and we have learned what is useful and what is not, so we are looking into the possibility of a daemon-less version of HPLIP. > The underlying problem of my question is that because of the > daemons it is complicated to update HPLIP in a running system. > > The correct way to update HPLIP is: > /etc/init.d/cups stop > /etc/init.d/hplip stop > replace the installed HPLIP files with the files of the new > version /etc/init.d/hplip start /etc/init.d/cups start > > It is not possible to stop and start the services in an > automated way (e.g. via RPM preinstall and postinstall > scripts) because it is not possible to stop (and re-start) > the whole printing service in an automated way when only one > single printer driver package is to be updated because all > currently printing jobs would be interrupted and re-printed > from the very beginning which is not possible in particular > in the business environment. After an HPLIP update, you should be able to restart HPLIP with a single command. /etc/init.d/hplip restart As long as there are no HPLIP print jobs active, a CUPS stop/restart is not required. -dave > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf > Of Johannes Meixner > Sent: Monday, February 26, 2007 5:41 AM > To: hplip-devel@lists.sourceforge.net > Subject: [HPLIP-Devel] Why are the HPLIP daemons required? > > > Hello, > > perhaps it is a stupid question but I do not well understand > why HPLIP requires continuously running processes (i.e. daemons). > > The underlying problem of my question is that because of the > daemons it is complicated to update HPLIP in a running system. > > The correct way to update HPLIP is: > /etc/init.d/cups stop > /etc/init.d/hplip stop > replace the installed HPLIP files with the files of the new > version /etc/init.d/hplip start /etc/init.d/cups start > > It is not possible to stop and start the services in an > automated way (e.g. via RPM preinstall and postinstall > scripts) because it is not possible to stop (and re-start) > the whole printing service in an automated way when only one > single printer driver package is to be updated because all > currently printing jobs would be interrupted and re-printed > from the very beginning which is not possible in particular > in the business environment. > > Therefore I think about what the inevitable reason is which > requires continuously running processes but up to now I > didn't find such a reason. > > My thoughts up to now: > > 1) Mutual exclusion: > Mutual exclusion is needed when different users or processes > try to access a device at the same time (e.g. one user prints > while a second user wants to scan while a third user queries > the device status). > I think a usual lock file which contains device status info > should be sufficient so that the other users can be informed > if and why the device is currently in use. > > 2) Track the device status: > Why continuously track the device status when no user or > process asks for it? > Shouldn't it be sufficient to query the device status from > the lock file (if another process is currently accessing the > device) or if no such file exists query it anew directly from > the device? > > 3) Access permissions: > Daemons which run as root seem to solve any access permission > problem but actually they ignore any access permission policy. > If there were no "root"-daemons, the established access > permission policies of each Linux distribution could be used > even for HPLIP. > > > Kind Regards > Johannes Meixner > -- > SUSE LINUX Products GmbH, Maxfeldstrasse 5, 90409 Nuernberg, > Germany AG Nuernberg, HRB 16746, GF: Markus Rex > > -------------------------------------------------------------- > ----------- > Take Surveys. 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