Class DvdWriter
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object --+
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DvdWriter
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
,
growisofs
and dvd+rw-mediainfo
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:
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MEDIA_DVDPLUSR
: DVD+R media (4.4 GB capacity)
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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.
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__init__(self,
device,
scsiId=None,
driveSpeed=None,
mediaType=2,
noEject=True,
unittest=True)
Initializes a DVD writer object. |
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isRewritable(self)
Indicates whether the media is rewritable per configuration. |
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refreshMedia(self)
Opens and then immediately closes the device's tray, to refresh
the device's idea of the media. |
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writeImage(self,
imagePath=None,
newDisc=True,
writeMulti=True)
Writes an ISO image to the media in the device. |
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_writeImage(self,
newDisc,
imagePath,
entries,
mediaLabel=None)
Writes an image to disc using either an entries list or an ISO
image on disk. |
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_getDevice(self)
Property target used to get the device value. |
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_getScsiId(self)
Property target used to get the SCSI id value. |
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_getHardwareId(self)
Property target used to get the hardware id value. |
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_getDriveSpeed(self)
Property target used to get the drive speed. |
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_getMedia(self)
Property target used to get the media description. |
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_getDeviceHasTray(self)
Property target used to get the device-has-tray flag. |
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_getDeviceCanEject(self)
Property target used to get the device-can-eject flag. |
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Inherited from object :
__delattr__ ,
__getattribute__ ,
__hash__ ,
__new__ ,
__reduce__ ,
__reduce_ex__ ,
__repr__ ,
__setattr__ ,
__str__
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_buildWriteArgs(newDisc,
hardwareId,
driveSpeed,
imagePath,
entries,
mediaLabel=None,
dryRun=True)
Builds a list of arguments to be passed to a
growisofs command. |
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device
Filesystem device name for this writer.
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scsiId
SCSI id for the device (saved for reference only).
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hardwareId
Hardware id for this writer (always the device path).
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driveSpeed
Speed at which the drive writes.
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media
Definition of media that is expected to be in the device.
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deviceHasTray
Indicates whether the device has a media tray.
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deviceCanEject
Indicates whether the device supports ejecting its media.
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Inherited from object :
__class__
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__init__(self,
device,
scsiId=None,
driveSpeed=None,
mediaType=2,
noEject=True,
unittest=True)
(Constructor)
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Initializes a DVD writer object.
Since growisofs can only address devices using the device
path (i.e. /dev/dvd ), the hardware id will always be set
based on the device. If passed in, it will be saved for reference
purposes only.
We have no way to query the device to ask whether it has a tray or can
be safely opened and closed. So, the noEject flag is used
to set these values. If noEject=False , then we assume a
tray exists and open/close is safe. If noEject=True , then
we assume that there is no tray and open/close is not safe.
- Parameters:
device (Absolute path to a filesystem device, i.e.
/dev/dvd ) - Filesystem device associated with this writer.
scsiId (If provided, SCSI id in the form
[<method>:]scsibus,target,lun ) - SCSI id for the device (optional, for reference only).
driveSpeed (Use 2 for 2x device, etc. or None to
use device default.) - Speed at which the drive writes.
mediaType (One of the valid media type as discussed above.) - Type of the media that is assumed to be in the drive.
noEject (Boolean true/false) - Tells Cedar Backup that the device cannot safely be
ejected
unittest (Boolean true/false) - Turns off certain validations, for use in unit testing.
- Raises:
ValueError - If the device is not valid for some reason.
ValueError - If the SCSI id is not in a valid form.
ValueError - If the drive speed is not an integer >= 1.
- Overrides:
object.__init__
Note:
The unittest parameter should never be set to
True outside of Cedar Backup code. It is intended for
use in unit testing Cedar Backup internals and has no other
sensible purpose.
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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.
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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.
- Raises:
IOError - If there is an error talking to the device.
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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.
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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.
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.
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initializeImage(self,
newDisc,
tmpdir,
mediaLabel=None)
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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
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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 .
- 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
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writeImage(self,
imagePath=None,
newDisc=True,
writeMulti=True)
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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.
- 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
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.
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Resets (overrides) the newDisc flag on the internal image.
- Parameters:
newDisc - New disc flag to set
- Raises:
ValueError - If initializeImage() was not previously called
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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
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_writeImage(self,
newDisc,
imagePath,
entries,
mediaLabel=None)
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Writes an image to disc using either an entries list or an ISO image
on disk.
Callers are assumed to have done validation on paths, etc. before
calling this method.
- Parameters:
newDisc - Indicates whether the disc should be re-initialized
imagePath - Path to an ISO image on disk, or c{None} to use
entries
entries - Mapping from path to graft point, or None to use
imagePath
- Raises:
IOError - If the media could not be written to for some reason.
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_getEstimatedImageSize(entries)
Static Method
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Gets the estimated size of a set of image entries.
This is implemented in terms of the IsoImage class. The
returned value is calculated by adding a "fudge factor" to the
value from IsoImage . This fudge factor was determined by
experimentation and is conservative -- the actual image could be as much
as 450 blocks smaller under some circumstances.
- Parameters:
entries - Dictionary mapping path to graft point.
- Returns:
- Total estimated size of image, in bytes.
- Raises:
ValueError - If there are no entries in the dictionary
ValueError - If any path in the dictionary does not exist
IOError - If there is a problem calling mkisofs .
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Search for an "overburn" error message in
growisofs output.
The growisofs command returns a non-zero exit code and
puts a message into the output -- even on a dry run -- if there is not
enough space on the media. This is called an "overburn"
condition.
The error message looks like this:
:-( /dev/cdrom: 894048 blocks are free, 2033746 to be written!
This method looks for the overburn error message anywhere in the
output. If a matching error message is found, an IOError
exception is raised containing relevant information about the problem.
Otherwise, the method call returns normally.
- Parameters:
output - List of output lines to search, as from
executeCommand
- Raises:
IOError - If an overburn condition is found.
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_buildWriteArgs(newDisc,
hardwareId,
driveSpeed,
imagePath,
entries,
mediaLabel=None,
dryRun=True)
Static Method
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Builds a list of arguments to be passed to a growisofs
command.
The arguments will either cause growisofs to write the
indicated image file to disc, or will pass growisofs a list
of directories or files that should be written to disc.
If a new image is created, it will always be created with Rock Ridge
extensions (-r). A volume name will be applied (-V) if
mediaLabel is not None .
- Parameters:
newDisc - Indicates whether the disc should be re-initialized
hardwareId - Hardware id for the device
driveSpeed - Speed at which the drive writes.
imagePath - Path to an ISO image on disk, or c{None} to use
entries
entries - Mapping from path to graft point, or None to use
imagePath
mediaLabel - Media label to set on the image, if any
dryRun - Says whether to make this a dry run (for checking
capacity)
- Returns:
- List suitable for passing to util.executeCommand as
args .
- Raises:
ValueError - If caller does not pass one or the other of imagePath or
entries.
Notes:
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If we write an existing image to disc, then the mediaLabel is
ignored. The media label is an attribute of the image, and should
be set on the image when it is created.
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We always pass the undocumented option
-use-the-force-like=tty to growisofs. Without this
option, growisofs will refuse to execute certain actions when
running from cron. A good example is -Z, which happily overwrites
an existing DVD from the command-line, but fails when run from
cron. It took a while to figure that out, since it worked every
time I tested it by hand. :(
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Retrieves the number of sectors used on the current media.
This is a little ugly. We need to call growisofs in
"dry-run" mode and parse some information from its output.
However, to do that, we need to create a dummy file that we can pass to
the command -- and we have to make sure to remove it later.
Once growisofs has been run, then we call
_parseSectorsUsed to parse the output and calculate the
number of sectors used on the media.
- Returns:
- Number of sectors used on the media
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Parse sectors used information out of growisofs
output.
The first line of a growisofs run looks something like this:
Executing 'mkisofs -C 973744,1401056 -M /dev/fd/3 -r -graft-points music4/=music | builtin_dd of=/dev/cdrom obs=32k seek=87566'
Dmitry has determined that the seek value in this line gives us
information about how much data has previously been written to the media.
That value multiplied by 16 yields the number of sectors used.
If the seek line cannot be found in the output, then sectors used of
zero is assumed.
- Returns:
- Sectors used on the media, as a floating point number.
- Raises:
ValueError - If the output cannot be parsed properly.
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