@@ -6,7 +6,7 @@ Using the RAM disk block device with Lin
1) Overview
2) Kernel Command Line Parameters
- 3) Using "rdev -r"
+ 3) Using "rdev"
4) An Example of Creating a Compressed RAM Disk
@@ -59,51 +59,27 @@ default is 4096 (4 MB).
rd_size
See ramdisk_size.
-3) Using "rdev -r"
-------------------
+3) Using "rdev"
+---------------
-The usage of the word (two bytes) that "rdev -r" sets in the kernel image is
-as follows. The low 11 bits (0 -> 10) specify an offset (in 1 k blocks) of up
-to 2 MB (2^11) of where to find the RAM disk (this used to be the size). Bit
-14 indicates that a RAM disk is to be loaded, and bit 15 indicates whether a
-prompt/wait sequence is to be given before trying to read the RAM disk. Since
-the RAM disk dynamically grows as data is being written into it, a size field
-is not required. Bits 11 to 13 are not currently used and may as well be zero.
-These numbers are no magical secrets, as seen below::
-
- ./arch/x86/kernel/setup.c:#define RAMDISK_IMAGE_START_MASK 0x07FF
- ./arch/x86/kernel/setup.c:#define RAMDISK_PROMPT_FLAG 0x8000
- ./arch/x86/kernel/setup.c:#define RAMDISK_LOAD_FLAG 0x4000
-
-Consider a typical two floppy disk setup, where you will have the
-kernel on disk one, and have already put a RAM disk image onto disk #2.
-
-Hence you want to set bits 0 to 13 as 0, meaning that your RAM disk
-starts at an offset of 0 kB from the beginning of the floppy.
-The command line equivalent is: "ramdisk_start=0"
-
-You want bit 14 as one, indicating that a RAM disk is to be loaded.
-The command line equivalent is: "load_ramdisk=1"
-
-You want bit 15 as one, indicating that you want a prompt/keypress
-sequence so that you have a chance to switch floppy disks.
-The command line equivalent is: "prompt_ramdisk=1"
-
-Putting that together gives 2^15 + 2^14 + 0 = 49152 for an rdev word.
-So to create disk one of the set, you would do::
-
- /usr/src/linux# cat arch/x86/boot/zImage > /dev/fd0
- /usr/src/linux# rdev /dev/fd0 /dev/fd0
- /usr/src/linux# rdev -r /dev/fd0 49152
+"rdev" is an obsolete, deprecated, antiquated utility that could be used
+to set the boot device in a Linux kernel image.
-If you make a boot disk that has LILO, then for the above, you would use::
+Instead of using rdev, just place the boot device information on the
+kernel command line and pass it to the kernel from the bootloader.
+
+You can also pass arguments to the kernel by setting FDARGS in
+arch/x86/boot/Makefile and specify in initrd image by setting FDINITRD in
+arch/x86/boot/Makefile.
- append = "ramdisk_start=0 load_ramdisk=1 prompt_ramdisk=1"
+Some of the kernel command line boot options that may apply here are::
-Since the default start = 0 and the default prompt = 1, you could use::
+ ramdisk_start=N
+ ramdisk_size=M
- append = "load_ramdisk=1"
+If you make a boot disk that has LILO, then for the above, you would use::
+ append = "ramdisk_start=N ramdisk_size=M"
4) An Example of Creating a Compressed RAM Disk
-----------------------------------------------
@@ -151,12 +127,9 @@ f) Put the RAM disk image onto the flopp
dd if=/tmp/ram_image.gz of=/dev/fd0 bs=1k seek=400
-g) Use "rdev" to set the boot device, RAM disk offset, prompt flag, etc.
- For prompt_ramdisk=1, load_ramdisk=1, ramdisk_start=400, one would
- have 2^15 + 2^14 + 400 = 49552::
-
- rdev /dev/fd0 /dev/fd0
- rdev -r /dev/fd0 49552
+g) Make sure that you have already specified the boot information in
+ FDARGS and FDINITRD or that you use a bootloader to pass kernel
+ command line boot options to the kernel.
That is it. You now have your boot/root compressed RAM disk floppy. Some
users may wish to combine steps (d) and (f) by using a pipe.
@@ -167,11 +140,14 @@ users may wish to combine steps (d) and
Changelog:
----------
+SEPT-2020 :
+
+ Removed usage of "rdev"
+
10-22-04 :
Updated to reflect changes in command line options, remove
obsolete references, general cleanup.
James Nelson (james4765@gmail.com)
-
12-95 :
Original Document
@@ -2441,8 +2441,7 @@
memblock=debug [KNL] Enable memblock debug messages.
- load_ramdisk= [RAM] List of ramdisks to load from floppy
- See Documentation/admin-guide/blockdev/ramdisk.rst.
+ load_ramdisk= [RAM] [Deprecated]
lockd.nlm_grace_period=P [NFS] Assign grace period.
Format: <integer>
@@ -3921,9 +3920,7 @@
Param: <number> - step/bucket size as a power of 2 for
statistical time based profiling.
- prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
- before loading.
- See Documentation/admin-guide/blockdev/ramdisk.rst.
+ prompt_ramdisk= [RAM] [Deprecated]
prot_virt= [S390] enable hosting protected virtual machines
isolated from the hypervisor (if hardware supports
@@ -3981,6 +3978,8 @@
ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
See Documentation/admin-guide/blockdev/ramdisk.rst.
+ ramdisk_start= [RAM] RAM disk image start address
+
random.trust_cpu={on,off}
[KNL] Enable or disable trusting the use of the
CPU's random number generator (if available) to
Remove use of "rdev" from blockdev/ramdisk.rst and update admin-guide/kernel-parameters.txt. "rdev" is considered antiquated, ancient, archaic, obsolete, deprecated {choose any or all}. "rdev" was removed from util-linux in 2010: https://git.kernel.org/pub/scm/utils/util-linux/util-linux.git/commit/?id=a3e40c14651fccf18e7954f081e601389baefe3f Signed-off-by: Randy Dunlap <rdunlap@infradead.org> Cc: Karel Zak <kzak@redhat.com> Cc: Paul Gortmaker <paul.gortmaker@windriver.com> Cc: Jens Axboe <axboe@kernel.dk> Cc: linux-block@vger.kernel.org Cc: Alexander Viro <viro@zeniv.linux.org.uk> Cc: Martin Mares <mj@ucw.cz> Cc: linux-video@atrey.karlin.mff.cuni.cz Cc: "H. Peter Anvin" <hpa@zytor.com> Cc: Jonathan Corbet <corbet@lwn.net> Cc: linux-doc@vger.kernel.org --- v2: modify Changelog date format. No email address for these: nCc: Werner Almesberger nCc: Stephen Tweedie nCc: Peter MacDonald Documentation/admin-guide/blockdev/ramdisk.rst | 70 ++++---------- Documentation/admin-guide/kernel-parameters.txt | 9 - 2 files changed, 27 insertions(+), 52 deletions(-)