From 6b99e6e6aa6237b3f45ea24327fd3cb132b365cd Mon Sep 17 00:00:00 2001 From: Randy Dunlap Date: Thu, 17 Sep 2020 18:56:40 -0700 Subject: [PATCH] Documentation/admin-guide: blockdev/ramdisk: remove use of "rdev" 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 Cc: Karel Zak Cc: Paul Gortmaker Cc: Jens Axboe Cc: linux-block@vger.kernel.org Cc: Alexander Viro Cc: Martin Mares Cc: linux-video@atrey.karlin.mff.cuni.cz Cc: "H. Peter Anvin" Cc: Jonathan Corbet Cc: linux-doc@vger.kernel.org Link: https://lore.kernel.org/r/20200918015640.8439-3-rdunlap@infradead.org Signed-off-by: Jonathan Corbet --- Documentation/admin-guide/blockdev/ramdisk.rst | 66 ++++++++----------------- Documentation/admin-guide/kernel-parameters.txt | 9 ++-- 2 files changed, 25 insertions(+), 50 deletions(-) diff --git a/Documentation/admin-guide/blockdev/ramdisk.rst b/Documentation/admin-guide/blockdev/ramdisk.rst index b7c2268..9ce6101 100644 --- a/Documentation/admin-guide/blockdev/ramdisk.rst +++ b/Documentation/admin-guide/blockdev/ramdisk.rst @@ -6,7 +6,7 @@ Using the RAM disk block device with Linux 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:: +"rdev" is an obsolete, deprecated, antiquated utility that could be used +to set the boot device in a Linux kernel image. - ./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 +Instead of using rdev, just place the boot device information on the +kernel command line and pass it to the kernel from the bootloader. -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. +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. -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" +Some of the kernel command line boot options that may apply here are:: -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 + ramdisk_start=N + ramdisk_size=M If you make a boot disk that has LILO, then for the above, you would use:: - append = "ramdisk_start=0 load_ramdisk=1 prompt_ramdisk=1" - -Since the default start = 0 and the default prompt = 1, you could use:: - - append = "load_ramdisk=1" - + 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 floppy, after the kernel. Use an offset 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 (f) by using a pipe. 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 diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index 280b564..835965b 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -2453,8 +2453,7 @@ 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: @@ -3933,9 +3932,7 @@ Param: - 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 @@ -3993,6 +3990,8 @@ 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 -- 2.7.4