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Signed-off-by: Pali Rohár <pali@kernel.org> Link: https://lore.kernel.org/r/20220210192200.30828-1-pali@kernel.org Signed-off-by: Jonathan Corbet <corbet@lwn.net>
140 lines
3.9 KiB
ReStructuredText
140 lines
3.9 KiB
ReStructuredText
==============
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Packet writing
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==============
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Getting started quick
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---------------------
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- Select packet support in the block device section and UDF support in
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the file system section.
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- Compile and install kernel and modules, reboot.
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- You need the udftools package (pktsetup, mkudffs, cdrwtool).
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Download from https://github.com/pali/udftools
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- Grab a new CD-RW disc and format it (assuming CD-RW is hdc, substitute
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as appropriate)::
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# cdrwtool -d /dev/hdc -q
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- Setup your writer::
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# pktsetup dev_name /dev/hdc
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- Now you can mount /dev/pktcdvd/dev_name and copy files to it. Enjoy::
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# mount /dev/pktcdvd/dev_name /cdrom -t udf -o rw,noatime
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Packet writing for DVD-RW media
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-------------------------------
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DVD-RW discs can be written to much like CD-RW discs if they are in
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the so called "restricted overwrite" mode. To put a disc in restricted
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overwrite mode, run::
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# dvd+rw-format /dev/hdc
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You can then use the disc the same way you would use a CD-RW disc::
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# pktsetup dev_name /dev/hdc
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# mount /dev/pktcdvd/dev_name /cdrom -t udf -o rw,noatime
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Packet writing for DVD+RW media
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-------------------------------
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According to the DVD+RW specification, a drive supporting DVD+RW discs
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shall implement "true random writes with 2KB granularity", which means
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that it should be possible to put any filesystem with a block size >=
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2KB on such a disc. For example, it should be possible to do::
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# dvd+rw-format /dev/hdc (only needed if the disc has never
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been formatted)
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# mkudffs /dev/hdc
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# mount /dev/hdc /cdrom -t udf -o rw,noatime
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However, some drives don't follow the specification and expect the
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host to perform aligned writes at 32KB boundaries. Other drives do
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follow the specification, but suffer bad performance problems if the
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writes are not 32KB aligned.
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Both problems can be solved by using the pktcdvd driver, which always
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generates aligned writes::
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# dvd+rw-format /dev/hdc
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# pktsetup dev_name /dev/hdc
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# mkudffs /dev/pktcdvd/dev_name
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# mount /dev/pktcdvd/dev_name /cdrom -t udf -o rw,noatime
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Packet writing for DVD-RAM media
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--------------------------------
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DVD-RAM discs are random writable, so using the pktcdvd driver is not
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necessary. However, using the pktcdvd driver can improve performance
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in the same way it does for DVD+RW media.
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Notes
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-----
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- CD-RW media can usually not be overwritten more than about 1000
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times, so to avoid unnecessary wear on the media, you should always
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use the noatime mount option.
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- Defect management (ie automatic remapping of bad sectors) has not
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been implemented yet, so you are likely to get at least some
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filesystem corruption if the disc wears out.
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- Since the pktcdvd driver makes the disc appear as a regular block
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device with a 2KB block size, you can put any filesystem you like on
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the disc. For example, run::
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# /sbin/mke2fs /dev/pktcdvd/dev_name
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to create an ext2 filesystem on the disc.
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Using the pktcdvd sysfs interface
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---------------------------------
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Since Linux 2.6.20, the pktcdvd module has a sysfs interface
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and can be controlled by it. For example the "pktcdvd" tool uses
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this interface. (see http://tom.ist-im-web.de/linux/software/pktcdvd )
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"pktcdvd" works similar to "pktsetup", e.g.::
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# pktcdvd -a dev_name /dev/hdc
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# mkudffs /dev/pktcdvd/dev_name
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# mount -t udf -o rw,noatime /dev/pktcdvd/dev_name /dvdram
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# cp files /dvdram
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# umount /dvdram
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# pktcdvd -r dev_name
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For a description of the sysfs interface look into the file:
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Documentation/ABI/testing/sysfs-class-pktcdvd
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Using the pktcdvd debugfs interface
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-----------------------------------
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To read pktcdvd device infos in human readable form, do::
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# cat /sys/kernel/debug/pktcdvd/pktcdvd[0-7]/info
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For a description of the debugfs interface look into the file:
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Documentation/ABI/testing/debugfs-pktcdvd
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Links
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-----
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See http://fy.chalmers.se/~appro/linux/DVD+RW/ for more information
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about DVD writing.
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