On Sunday 27 January 2008, Borislav Petkov wrote:
Also, cleanup whitespace and update comments.
Signed-off-by: Borislav Petkov [EMAIL PROTECTED]
applied with some changes
---
Documentation/ide/ChangeLog.ide-tape.1995-2002 | 405 +++
drivers/ide/ide-tape.c | 414
+---
2 files changed, 409 insertions(+), 410 deletions(-)
diff --git a/Documentation/ide/ChangeLog.ide-tape.1995-2002
b/Documentation/ide/ChangeLog.ide-tape.1995-2002
new file mode 100644
index 000..e406762
--- /dev/null
+++ b/Documentation/ide/ChangeLog.ide-tape.1995-2002
@@ -0,0 +1,405 @@
+/*
+ * IDE ATAPI streaming tape driver.
+ *
+ * This driver is a part of the Linux ide driver and works in co-operation
+ * with drivers/block/ide.c.
I removed incorrect reference to drivers/block/ide.c
+ * The driver, in co-operation with ide.c, basically traverses the
+ * request-list for the block device interface. The character device
+ * interface, on the other hand, creates new requests, adds them
+ * to the request-list of the block device, and waits for their completion.
+ *
+ * Pipelined operation mode is now supported on both reads and writes.
+ *
+ * The block device major and minor numbers are determined from the
+ * tape's relative position in the ide interfaces, as explained in ide.c.
+ *
+ * The character device interface consists of the following devices:
+ *
+ * ht0 major 37, minor 0 first IDE tape, rewind on
close.
+ * ht1 major 37, minor 1 second IDE tape, rewind on
close.
+ * ...
+ * nht0 major 37, minor 128 first IDE tape, no rewind on
close.
+ * nht1 major 37, minor 129 second IDE tape, no rewind on
close.
+ * ...
+ *
+ * The general magnetic tape commands compatible interface, as defined by
+ * include/linux/mtio.h, is accessible through the character device.
+ *
+ * General ide driver configuration options, such as the interrupt-unmask
+ * flag, can be configured by issuing an ioctl to the block device interface,
+ * as any other ide device.
+ *
+ * Our own ide-tape ioctl's can be issued to either the block device or
+ * the character device interface.
+ *
+ * Maximal throughput with minimal bus load will usually be achieved in the
+ * following scenario:
+ *
+ * 1. ide-tape is operating in the pipelined operation mode.
+ * 2. No buffering is performed by the user backup program.
the above is not the part of the changelog
[...]
+ * Here are some words from the first releases of hd.c, which are quoted
+ * in ide.c and apply here as well:
+ *
+ * | Special care is recommended. Have Fun!
[...]
ditto
+ * An overview of the pipelined operation mode.
+ *
+ * In the pipelined write mode, we will usually just add requests to our
+ * pipeline and return immediately, before we even start to service them. The
+ * user program will then have enough time to prepare the next request while
+ * we are still busy servicing previous requests. In the pipelined read mode,
+ * the situation is similar - we add read-ahead requests into the pipeline,
+ * before the user even requested them.
+ *
+ * The pipeline can be viewed as a safety net which will be activated when
+ * the system load is high and prevents the user backup program from keeping
up
+ * with the current tape speed. At this point, the pipeline will get
+ * shorter and shorter but the tape will still be streaming at the same
speed.
+ * Assuming we have enough pipeline stages, the system load will hopefully
+ * decrease before the pipeline is completely empty, and the backup program
+ * will be able to catch up and refill the pipeline again.
+ *
+ * When using the pipelined mode, it would be best to disable any type of
+ * buffering done by the user program, as ide-tape already provides all the
+ * benefits in the kernel, where it can be done in a more efficient way.
+ * As we will usually not block the user program on a request, the most
+ * efficient user code will then be a simple read-write-read-... cycle.
+ * Any additional logic will usually just slow down the backup process.
+ *
+ * Using the pipelined mode, I get a constant over 400 KBps throughput,
+ * which seems to be the maximum throughput supported by my tape.
+ *
+ * However, there are some downfalls:
+ *
+ * 1. We use memory (for data buffers) in proportional to the number
+ * of pipeline stages (each stage is about 26 KB with my tape).
+ * 2. In the pipelined write mode, we cheat and postpone error codes
+ * to the user task. In read mode, the actual tape position
+ * will be a bit further than the last requested block.
+ *
+ * Concerning (1):
+ *
+ * 1. We allocate stages dynamically only when we need them. When
+ * we don't need them, we don't consume additional memory. In
+ *
