CedarBackup3.writers.dvdwriter

Provides functionality related to DVD writer devices.

Module Attributes

CedarBackup3.writers.dvdwriter.MEDIA_DVDPLUSR

Constant representing DVD+R media

CedarBackup3.writers.dvdwriter.MEDIA_DVDPLUSRW

Constant representing DVD+RW media

author

Kenneth J. Pronovici <pronovic@ieee.org>

author

Dmitry Rutsky <rutsky@inbox.ru>

Module Contents

CedarBackup3.writers.dvdwriter.logger

CedarBackup3.writers.dvdwriter.MEDIA_DVDPLUSR = 1

CedarBackup3.writers.dvdwriter.MEDIA_DVDPLUSRW = 2

CedarBackup3.writers.dvdwriter.GROWISOFS_COMMAND = ['growisofs']

CedarBackup3.writers.dvdwriter.EJECT_COMMAND = ['eject']

class CedarBackup3.writers.dvdwriter.MediaDefinition(mediaType)

Bases: object

Class encapsulating information about DVD media definitions.

The following media types are accepted:

• MEDIA_DVDPLUSR: DVD+R media (4.4 GB capacity)

• MEDIA_DVDPLUSRW: DVD+RW media (4.4 GB capacity)

Note that the capacity attribute returns capacity in terms of ISO sectors (util.ISO_SECTOR_SIZE). This is for compatibility with the CD writer functionality.

The capacities are 4.4 GB because Cedar Backup deals in “true” gigabytes of 1024*1024*1024 bytes per gigabyte.

mediaType

rewritable

capacity

class CedarBackup3.writers.dvdwriter.MediaCapacity(bytesUsed, bytesAvailable)

Bases: object

Class encapsulating information about DVD media capacity.

Space used and space available do not include any information about media lead-in or other overhead.

bytesUsed

bytesAvailable

totalCapacity

utilized

__str__()

Informal string representation for class instance.

class CedarBackup3.writers.dvdwriter.DvdWriter(device, scsiId=None, driveSpeed=None, mediaType=MEDIA_DVDPLUSRW, noEject=False, refreshMediaDelay=0, ejectDelay=0, unittest=False)

Bases: object

Class representing a device that knows how to write some kinds of DVD media.

Summary

This is a class representing a device that knows how to write some kinds of DVD media. It provides common operations for the device, such as ejecting the media and writing data to the media.

This class is implemented in terms of the eject and growisofs utilities, all of which should be available on most UN*X platforms.

Image Writer Interface

The following methods make up the “image writer” interface shared with other kinds of writers:

__init__
initializeImage()
addImageEntry()
writeImage()
setImageNewDisc()
retrieveCapacity()
getEstimatedImageSize()

Only these methods will be used by other Cedar Backup functionality that expects a compatible image writer.

The media attribute is also assumed to be available.

Unlike the CdWriter, the DvdWriter can only operate in terms of filesystem devices, not SCSI devices. So, although the constructor interface accepts a SCSI device parameter for the sake of compatibility, it’s not used.

Media Types

This class knows how to write to DVD+R and DVD+RW media, represented by the following constants:

• MEDIA_DVDPLUSR: DVD+R media (4.4 GB capacity)

• MEDIA_DVDPLUSRW: DVD+RW media (4.4 GB capacity)

The difference is that DVD+RW media can be rewritten, while DVD+R media cannot be (although at present, DvdWriter does not really differentiate between rewritable and non-rewritable media).

The capacities are 4.4 GB because Cedar Backup deals in “true” gigabytes of 1024*1024*1024 bytes per gigabyte.

The underlying growisofs utility does support other kinds of media (including DVD-R, DVD-RW and BlueRay) which work somewhat differently than standard DVD+R and DVD+RW media. I don’t support these other kinds of media because I haven’t had any opportunity to work with them. The same goes for dual-layer media of any type.

Device Attributes vs. Media Attributes

As with the cdwriter functionality, a given dvdwriter instance has two different kinds of attributes associated with it. I call these device attributes and media attributes.

Device attributes are things which can be determined without looking at the media. Media attributes are attributes which vary depending on the state of the media. In general, device attributes are available via instance variables and are constant over the life of an object, while media attributes can be retrieved through method calls.

Compared to cdwriters, dvdwriters have very few attributes. This is due to differences between the way growisofs works relative to cdrecord.

Media Capacity

One major difference between the cdrecord/mkisofs utilities used by the cdwriter class and the growisofs utility used here is that the process of estimating remaining capacity and image size is more straightforward with cdrecord/mkisofs than with growisofs.

In this class, remaining capacity is calculated by asking doing a dry run of growisofs and grabbing some information from the output of that command. Image size is estimated by asking the IsoImage class for an estimate and then adding on a “fudge factor” determined through experimentation.

Testing

It’s rather difficult to test this code in an automated fashion, even if you have access to a physical DVD writer drive. It’s even more difficult to test it if you are running on some build daemon (think of a Debian autobuilder) which can’t be expected to have any hardware or any media that you could write to.

Because of this, some of the implementation below is in terms of static methods that are supposed to take defined actions based on their arguments. Public methods are then implemented in terms of a series of calls to simplistic static methods. This way, we can test as much as possible of the “difficult” functionality via testing the static methods, while hoping that if the static methods are called appropriately, things will work properly. It’s not perfect, but it’s much better than no testing at all.

device

scsiId

hardwareId

driveSpeed

media

deviceHasTray

deviceCanEject

refreshMediaDelay

ejectDelay

isRewritable()

Indicates whether the media is rewritable per configuration.

retrieveCapacity(entireDisc=False)

Retrieves capacity for the current media in terms of a MediaCapacity object.

If entireDisc is passed in as True, the capacity will be for the entire disc, as if it were to be rewritten from scratch. The same will happen if the disc can’t be read for some reason. Otherwise, the capacity will be calculated by subtracting the sectors currently used on the disc, as reported by growisofs itself.

Parameters

entireDisc (Boolean true/false) – Indicates whether to return capacity for entire disc

Returns

MediaCapacity object describing the capacity of the media

Raises

• ValueError – If there is a problem parsing the growisofs output

• IOError – If the media could not be read for some reason

initializeImage(newDisc, tmpdir, mediaLabel=None)

Initializes the writer’s associated ISO image.

This method initializes the image instance variable so that the caller can use the addImageEntry method. Once entries have been added, the writeImage method can be called with no arguments.

Parameters

• newDisc (Boolean true/false) – Indicates whether the disc should be re-initialized

• tmpdir (String representing a directory path on disk) – Temporary directory to use if needed

• mediaLabel (String, no more than 25 characters long) – Media label to be applied to the image, if any

addImageEntry(path, graftPoint)

Adds a filepath entry to the writer’s associated ISO image.

The contents of the filepath – but not the path itself – will be added to the image at the indicated graft point. If you don’t want to use a graft point, just pass None.

Note: Before calling this method, you must call initializeImage.

Parameters

• path (String representing a path on disk) – File or directory to be added to the image

• graftPoint (String representing a graft point path, as described above) – Graft point to be used when adding this entry

Raises

• ValueError – If initializeImage() was not previously called

• ValueError – If the path is not a valid file or directory

setImageNewDisc(newDisc)

Resets (overrides) the newDisc flag on the internal image. :param newDisc: New disc flag to set

Raises

ValueError – If initializeImage() was not previously called

getEstimatedImageSize()

Gets the estimated size of the image associated with the writer.

This is an estimate and is conservative. The actual image could be as much as 450 blocks (sectors) smaller under some circmstances.

Returns

Estimated size of the image, in bytes

Raises

• IOError – If there is a problem calling mkisofs

• ValueError – If initializeImage() was not previously called

openTray()

Opens the device’s tray and leaves it open.

This only works if the device has a tray and supports ejecting its media. We have no way to know if the tray is currently open or closed, so we just send the appropriate command and hope for the best. If the device does not have a tray or does not support ejecting its media, then we do nothing.

Starting with Debian wheezy on my backup hardware, I started seeing consistent problems with the eject command. I couldn’t tell whether these problems were due to the device management system or to the new kernel (3.2.0). Initially, I saw simple eject failures, possibly because I was opening and closing the tray too quickly. I worked around that behavior with the new ejectDelay flag.

Later, I sometimes ran into issues after writing an image to a disc: eject would give errors like “unable to eject, last error: Inappropriate ioctl for device”. Various sources online (like Ubuntu bug #875543) suggested that the drive was being locked somehow, and that the workaround was to run ‘eject -i off’ to unlock it. Sure enough, that fixed the problem for me, so now it’s a normal error-handling strategy.

Raises

IOError – If there is an error talking to the device

unlockTray()

Unlocks the device’s tray via ‘eject -i off’. :raises IOError: If there is an error talking to the device

closeTray()

Closes the device’s tray.

This only works if the device has a tray and supports ejecting its media. We have no way to know if the tray is currently open or closed, so we just send the appropriate command and hope for the best. If the device does not have a tray or does not support ejecting its media, then we do nothing.

Raises

IOError – If there is an error talking to the device

refreshMedia()

Opens and then immediately closes the device’s tray, to refresh the device’s idea of the media.

Sometimes, a device gets confused about the state of its media. Often, all it takes to solve the problem is to eject the media and then immediately reload it. (There are also configurable eject and refresh media delays which can be applied, for situations where this makes a difference.)

This only works if the device has a tray and supports ejecting its media. We have no way to know if the tray is currently open or closed, so we just send the appropriate command and hope for the best. If the device does not have a tray or does not support ejecting its media, then we do nothing. The configured delays still apply, though.

Raises

IOError – If there is an error talking to the device

writeImage(imagePath=None, newDisc=False, writeMulti=True)

Writes an ISO image to the media in the device.

If newDisc is passed in as True, we assume that the entire disc will be re-created from scratch. Note that unlike CdWriter, DvdWriter does not blank rewritable media before reusing it; however, growisofs is called such that the media will be re-initialized as needed.

If imagePath is passed in as None, then the existing image configured with initializeImage() will be used. Under these circumstances, the passed-in newDisc flag will be ignored and the value passed in to initializeImage() will apply instead.

The writeMulti argument is ignored. It exists for compatibility with the Cedar Backup image writer interface.

Note: The image size indicated in the log (“Image size will be…”) is an estimate. The estimate is conservative and is probably larger than the actual space that dvdwriter will use.

Parameters

• imagePath (String representing a path on disk) – Path to an ISO image on disk, or None to use writer’s image

• newDisc (Boolean true/false) – Indicates whether the disc should be re-initialized

• writeMulti (Boolean true/false) – Unused

Raises

• ValueError – If the image path is not absolute

• ValueError – If some path cannot be encoded properly

• IOError – If the media could not be written to for some reason

• ValueError – If no image is passed in and initializeImage() was not previously called