Reservation

Introduction

After the director set up a job on the SD and after running any run before scripts, it will then issue a “use” command to tell the SD what storage device it wants to use. The SD then checks the list of devices the director sent and tries to reserve a suitable device. In the end the SD either tells the director which device to use or that there is no device available for the job.

There is a so-called reservation context that is passed to every function that has a swimlane in this diagram. This context is basically a bunch of flags that are set and cleared to change the behaviour of the rest of the code.

For example CanReserveDevice() from the second diagram sets the flag low_use_drive which is then evaluated in UseDeviceCmd().

Diagram Conventions

Each swimlane denotes a separate function.

.. uml::
:caption: Diagram legend

@startuml
#aqua:reservation context is read or set;
detach
#limegreen:Decision based on configuration directive;
detach
#tomato:Control flow broken;
detach
(M)
note right
goto or jump-mark
end note
detach
:Read read data from the network<
detach
:Send data to the network>
detach
:Call another function|
detach
:Remote procedure call/

@enduml

UseDeviceCmd

This function reads the list of storages and devices the director is willing to use for this job. Afterwards several different methods of finding a device to reseve are used. If no device could be reserved the function waits for up to a minute or until ReleaseDeviceCond() is called and then tries again.

$.. uml:: :caption: Control flow of UseDeviceCmd() @startuml 'BEGIN macros !definelong RESERVE_DEVICE() :ReserveDevice()| !enddefinelong !definelong AUTOCHANGER() partition autochanger { while (with each device in autochanger device) #limegreen:if (device autoselect?) then (yes) RESERVE_DEVICE() if (have_device?) then (yes) #tomato:return; detach endif endif endwhile } !enddefinelong !definelong PLAIN_DEVICE() partition plain_device { RESERVE_DEVICE() note right try to reserve the named device end note if (have_device?) then (yes) #tomato:return; detach endif #limegreen:if (DeviceReserveByMediatype) then(yes) while (each device with matching media_type) RESERVE_DEVICE() if (have_device?) then (yes) #tomato:return; detach endif endwhile endif } !enddefinelong !definelong MOUNTED_VOLUMES() partition mounted_volumes { if (append?) then(yes) while(with each mounted volume) :ask director if volume is ok/ if (volume ok?) then(yes) :find device for volume; RESERVE_DEVICE() if (have_device?) then (yes) #tomato:return; detach endif endif endwhile endif } !enddefinelong 'END macros |UseDeviceCmd| start partition read_data_from_director { repeat :storage specification< repeat :device specification< repeat while (more devices?) repeat while (more storages?) } repeat #aqua:clear suitable_device] #aqua:clear have_volume] #aqua:clear VolumeName] #aqua:clear any_drive] #limegreen:if (PreferMountedVols) then (no) #aqua:clear low_use_drive] #aqua:clear PreferMountedVols] #aqua:clear exact_match] #aqua:set autochanger_only] |FindSuitableDeviceForJob| while (with every device) |SearchResForDevice| AUTOCHANGER() |FindSuitableDeviceForJob| endwhile |UseDeviceCmd| if (have_device) then (yes) stop else (no) #aqua:if (low_use_drive set?) then (yes) #aqua:set try_low_use_drive] |FindSuitableDeviceForJob| while (with every device) |SearchResForDevice| AUTOCHANGER() |FindSuitableDeviceForJob| endwhile |UseDeviceCmd| if (have_device) then (yes) stop endif #aqua:clear try_low_use_drive] endif #aqua:clear autochanger_only] |FindSuitableDeviceForJob| while (with every device) |SearchResForDevice| AUTOCHANGER() PLAIN_DEVICE() |FindSuitableDeviceForJob| endwhile |UseDeviceCmd| if (have_device) then (yes) stop endif endif else (yes) endif #aqua:set PreferMountedVols] #aqua:set exact_match] #aqua:clear autochanger_only] |FindSuitableDeviceForJob| MOUNTED_VOLUMES() while (with every device) |SearchResForDevice| AUTOCHANGER() PLAIN_DEVICE() |FindSuitableDeviceForJob| endwhile |UseDeviceCmd| if (have_device) then (yes) stop else (no) #aqua:clear exact_match] |FindSuitableDeviceForJob| MOUNTED_VOLUMES() while (with every device) |SearchResForDevice| AUTOCHANGER() PLAIN_DEVICE() |FindSuitableDeviceForJob| endwhile |UseDeviceCmd| if (have_device) then (yes) stop else (no) #aqua:set any_drive] |FindSuitableDeviceForJob| MOUNTED_VOLUMES() while (with every device) |SearchResForDevice| AUTOCHANGER() PLAIN_DEVICE() |FindSuitableDeviceForJob| endwhile |UseDeviceCmd| if (have_device) then (yes) stop else (no) if (attempt 3+?) then (yes) :wait 30 seconds; else (no) #aqua:if (suitable_device set?) then (yes) :WaitForDevice()| note right This will acquire a mutex to queue up multiple jobs waiting for a device. Then it waits up to 60 seconds for some other thread to call ReleaseDeviceCond() end note else (no) (F) detach endif endif endif endif endif repeat while (repeat forever) detach partition failed_to_reserve { (F) :no device message> stop } @enduml$

ReserveDevice

Here we see wether the media type matches and actually try to open the device. The actual reservation is delegated to ReserveDeviceForRead() or ReserveDeviceForAppend(). While the first one is more or less trivial, the latter one is really complicated.