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Date: Mon, 17 May 2010 13:13:48 -0500 From: Will Drewry <wad@...omium.org> To: Randy Dunlap <randy.dunlap@...cle.com> Cc: dm-devel@...hat.com, linux-kernel@...r.kernel.org, agk@...hat.com, snitzer@...hat.com Subject: Re: [RFC PATCH v2 2/2] init: boot to device-mapper targets without an initr* On Mon, May 17, 2010 at 11:47 AM, Randy Dunlap <randy.dunlap@...cle.com> wrote: > On Fri, 14 May 2010 20:41:41 -0500 Will Drewry wrote: > >> Add a dm= kernel parameter modeled after the md= parameter from >> do_mounts_md. It allows for device-mapper targets to be configured at >> boot time for use early in the boot process (as the root device or >> otherwise). > > dm=<blah> > documentation needs to be added to Documentation/kernel-parameters.txt and/or > Documentation/md.txt. Absolutely -- I've appended a proposed version below which I'll include in the next round. I'm not a lkml veteran, so if it makes sense to resend the full patchset again with it, I can. Otherwise, I'll wait for comments on the code too. >> The format is dm="name uuid ro,table line 1,table line 2,...". The >> parser expects the comma to be safe to use as a newline substitute but, >> otherwise, uses the normal separator of space. Some attempt has been >> made to make it forgiving of additional spaces (using skip_spaces()). > > This "space in the arg string" has been tested, right? Works for me so far. I've tested this on a user mode linux instance and a real x86 machine with the dm-linear target and a custom dm target (which I'll be mailing to dm-devel@ for feedback later this week). > It seems a bit odd to me. Most kernel parameter strings that I am familiar with > use punctuation for separating parameter parts. Yup - I agree. My first cut I used commas with an empty ,, delimiter as a new line. Then I ran across this in the source: kernel/params.c 76 /* You can use " around spaces, but can't escape ". */ 77 /* Hyphens and underscores equivalent in parameter names. */ 78 static char *next_arg(char *args, char **param, char **val) I will need to cross-check all the known dm targets to make sure that they don't expect quoted internal strings. In my first look, I didn't see any. However, I'm perfectly content with either approach so if there's a preference, I'll rework it to make it happen. This approach just maps more cleanly to the existing experience of configuring a mapped device. thanks! will documentation: dm= parameter documentation Add documentation for early mapped device creation without an initial rd. Signed-off-by: Will Drewry <wad@...omium.org> --- Documentation/device-mapper/boot.txt | 36 ++++++++++++++++++++++++++++++++++ Documentation/kernel-parameters.txt | 4 +++ 2 files changed, 40 insertions(+), 0 deletions(-) create mode 100644 Documentation/device-mapper/boot.txt diff --git a/Documentation/device-mapper/boot.txt b/Documentation/device-mapper/boot.txt new file mode 100644 index 0000000..00fb557 --- /dev/null +++ b/Documentation/device-mapper/boot.txt @@ -0,0 +1,36 @@ +Boot time creation of mapped devices +=================================== + +You can boot directly to a dm device using the following kernel command +line: + +dm="<name> <uuid> <ro>,table line 1,...,table line n" + +name = the name to associated with the device + after boot, udev, if used, will use that name to label + the device node. +uuid = may be 'none' or the UUID desired for the device. +ro = may be 0 or 1. If non-zero, the device and device table will be + marked read-only. + +Each table line may be as normal when using the dmsetup tool except for +two variations: +1. Any use of commas will be interpreted as a newline +2. Quotation marks cannot be escaped and cannot be used without + terminating the dm= argument. + +Unless renamed by udev, the device node created will be dm-0 as the +first minor number for the device-mapper is used during early creation. + +Example +======= + +- Booting to a linear array made up of user-mode linux block devices: + + dm="lroot none 0, 0 4096 linear 98:16 0, 4096 4096 linear 98:32 0" \ + root=/dev/dm-0 + +Will boot to a rw dm-linear target of 8192 sectors split across two +block devices identified by their major:minor numbers. After boot, udev +will rename this target to /dev/mapper/lroot (depending on the rules). +No uuid was assigned. diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt index 839b21b..9e22f8e 100644 --- a/Documentation/kernel-parameters.txt +++ b/Documentation/kernel-parameters.txt @@ -43,6 +43,7 @@ parameter is applicable: AVR32 AVR32 architecture is enabled. AX25 Appropriate AX.25 support is enabled. BLACKFIN Blackfin architecture is enabled. + DM Device mapper support is enabled. DRM Direct Rendering Management support is enabled. EDD BIOS Enhanced Disk Drive Services (EDD) is enabled EFI EFI Partitioning (GPT) is enabled @@ -654,6 +655,9 @@ and is between 256 and 4096 characters. It is defined in the file Disable PIN 1 of APIC timer Can be useful to work around chipset bugs. + dm= [DM] Allows early creation of a device-mapper device. + See Documentation/device-mapper/boot.txt. + dmasound= [HW,OSS] Sound subsystem buffers dma_debug=off If the kernel is compiled with DMA_API_DEBUG support, -- 1.7.0.4 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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