Re: [dm-devel] [PATCH v2] dm init: add dm-mod.waitfor to wait for asynchronously probed block devices

[Mike Snitzer <snitzer@redhat.com>]

On Thu, Nov 24 2022 at  5:35P -0500,
Peter Korsgaard <peter@korsgaard.com> wrote:

> >>>>> "Peter" == Peter Korsgaard <peter@korsgaard.com> writes:
> 
>  > Just calling wait_for_device_probe() is not enough to ensure that
>  > asynchronously probed block devices are available (E.G.  mmc, usb, ..), so
>  > add a "dm-mod.waitfor=<device1>[,..,<deviceN>]" parameter to get dm-init to
>  > explicitly wait for specific block devices before initializing the tables
>  > with logic similar to the rootwait logic in init/do_mounts.c.
> 
>  > E.G. with dm-verity on mmc with
>  > dm-mod.waitfor="PARTLABEL=hash-a,PARTLABEL=root-a"
> 
>  > [    0.671671] device-mapper: init: waiting for all devices to be available before creating mapped devices
>  > [    0.671679] device-mapper: init: waiting for PARTLABEL=hash-a
>  > [    0.710695] mmc0: new HS200 MMC card at address 0001
>  > [    0.711158] mmcblk0: mmc0:0001 004GA0 3.69 GiB
>  > [    0.715954] mmcblk0boot0: mmc0:0001 004GA0 partition 1 2.00 MiB
>  > [    0.722085] mmcblk0boot1: mmc0:0001 004GA0 partition 2 2.00 MiB
>  > [    0.728093] mmcblk0rpmb: mmc0:0001 004GA0 partition 3 512 KiB, chardev (249:0)
>  > [    0.738274]  mmcblk0: p1 p2 p3 p4 p5 p6 p7
>  > [    0.751282] device-mapper: init: waiting for PARTLABEL=root-a
>  > [    0.751306] device-mapper: init: all devices available
>  > [    0.751683] device-mapper: verity: sha256 using implementation "sha256-generic"
>  > [    0.759344] device-mapper: ioctl: dm-0 (vroot) is ready
>  > [    0.766540] VFS: Mounted root (squashfs filesystem) readonly on device 254:0.
> 
>  > Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
>  > ---
>  > Changes since v1:
>  > - Fix s/dm-init/dm-mod/ typo in documentation, drop trailing newline
> 
> Ping?
> 
> FYI: I was recently made aware that other patches fixing this issue
> (but less nice, E.G. with a fixed delay) have been posted in the past,
> so there seems to be a general need for something like this.
> 
> E.G:
> https://lore.kernel.org/all/20220406154631.277107-1-fabio.aiuto@amarulasolutions.com/
> 
> 
> 
>  >  .../admin-guide/device-mapper/dm-init.rst     |  8 +++++++
>  >  drivers/md/dm-init.c                          | 23 ++++++++++++++++++-
>  >  2 files changed, 30 insertions(+), 1 deletion(-)
> 
>  > diff --git a/Documentation/admin-guide/device-mapper/dm-init.rst b/Documentation/admin-guide/device-mapper/dm-init.rst
>  > index e5242ff17e9b..981d6a907699 100644
>  > --- a/Documentation/admin-guide/device-mapper/dm-init.rst
>  > +++ b/Documentation/admin-guide/device-mapper/dm-init.rst
>  > @@ -123,3 +123,11 @@ Other examples (per target):
>  >      0 1638400 verity 1 8:1 8:2 4096 4096 204800 1 sha256
>  >      fb1a5a0f00deb908d8b53cb270858975e76cf64105d412ce764225d53b8f3cfd
>  >      51934789604d1b92399c52e7cb149d1b3a1b74bbbcb103b2a0aaacbed5c08584
>  > +
>  > +For setups using device-mapper on top of asynchronously probed block
>  > +devices (MMC, USB, ..), it may be necessary to tell dm-init to
>  > +explicitly wait for them to become available before setting up the
>  > +device-mapper tables. This can be done with the "dm-mod.waitfor="
>  > +module parameter, which takes a list of devices to wait for::
>  > +
>  > +  dm-mod.waitfor=<device1>[,..,<deviceN>]
>  > diff --git a/drivers/md/dm-init.c b/drivers/md/dm-init.c
>  > index b0c45c6ebe0b..fc70b568e072 100644
>  > --- a/drivers/md/dm-init.c
>  > +++ b/drivers/md/dm-init.c
>  > @@ -8,6 +8,7 @@
>  >   */
>  
>  >  #include <linux/ctype.h>
>  > +#include <linux/delay.h>
>  >  #include <linux/device.h>
>  >  #include <linux/device-mapper.h>
>  >  #include <linux/init.h>
>  > @@ -18,12 +19,17 @@
>  >  #define DM_MAX_DEVICES 256
>  >  #define DM_MAX_TARGETS 256
>  >  #define DM_MAX_STR_SIZE 4096
>  > +#define DM_MAX_WAITFOR 256
>  
>  >  static char *create;
>  
>  > +static char *waitfor[DM_MAX_WAITFOR];
>  > +
>  >  /*
>  >   * Format: dm-mod.create=<name>,<uuid>,<minor>,<flags>,<table>[,<table>+][;<name>,<uuid>,<minor>,<flags>,<table>[,<table>+]+]
>  >   * Table format: <start_sector> <num_sectors> <target_type> <target_args>
>  > + * Block devices to wait for to become available before setting up tables:
>  > + * dm-mod.waitfor=<device1>[,..,<deviceN>]
>  >   *
>  >   * See Documentation/admin-guide/device-mapper/dm-init.rst for dm-mod.create="..." format
>  >   * details.
>  > @@ -266,7 +272,7 @@ static int __init dm_init_init(void)
>  >  	struct dm_device *dev;
>  >  	LIST_HEAD(devices);
>  >  	char *str;
>  > -	int r;
>  > +	int i, r;
>  
>  >  	if (!create)
>  >  		return 0;
>  > @@ -286,6 +292,18 @@ static int __init dm_init_init(void)
>  >  	DMINFO("waiting for all devices to be available before creating mapped devices");
>  >  	wait_for_device_probe();
>  
>  > +	for (i = 0; i < ARRAY_SIZE(waitfor); i++) {
>  > +		if (waitfor[i]) {
>  > +			DMINFO("waiting for %s", waitfor[i]);
>  > +
>  > +			while (!dm_get_dev_t(waitfor[i]))
>  > +				msleep(20);
>  > +		}
>  > +	}
>  > +
>  > +	if (waitfor[0])
>  > +		DMINFO("all devices available");
>  > +

Why 20?  Also, why is waiting indefinitely OK?  Would really like to
hear from other consumers of dm-init that this module param is useful
and needed.

Mike


>  >  	list_for_each_entry(dev, &devices, list) {
>  >  		if (dm_early_create(&dev->dmi, dev->table,
>  dev-> target_args_array))
>  > @@ -301,3 +319,6 @@ late_initcall(dm_init_init);
>  
>  >  module_param(create, charp, 0);
>  >  MODULE_PARM_DESC(create, "Create a mapped device in early boot");
>  > +
>  > +module_param_array(waitfor, charp, NULL, 0);
>  > +MODULE_PARM_DESC(waitfor, "Devices to wait for before setting up tables");
>  > -- 
> 
>  > 2.30.2
> 
> 
> -- 
> Bye, Peter Korsgaard
> 


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