Hi On Fri, 8 Nov 2024, Jooyung Han wrote: > Hi Mikulas, > > Would it be reasonable to allow this? Or, to reduce the risk or impact > on other users, how about introducing a flag for dm-linear constructor > to open a table device without setting the holder. I don't know how to > describe this, not-exclusive? The dm-linear constructor would look like > "<dev_path> <offset> [no_exclusive]", when "no_exclusive" is set, it > will open a table device without setting a holder. > > I'd like to get your opinion about this idea. Especially if there's any > risks about not setting the holder when opening a DM table device. > > Besides, there's one more question about dm-verity. Even though there's > a field named "data_start" (comment saying it's "data offset in 512-byte > sectors"): https://elixir.bootlin.com/linux/v6.11.4/source/drivers/md/dm-verity.h#L49, > it's not set in its constructor and always zero after initialization. I > think it's reasonable for the constructor to set it with an argument > passed. What do you think? Yes, we could set it in the constructor. > Thanks. I've created this (totally untested) patch that makes it possible to add a flag DM_OPEN_SHARED to the flags in the create ioctl - when the flag is used, all devices open by the specified device are open in a shared mode. Does the patch work for you? Mikulas From: Mikulas Patocka <mpatocka@xxxxxxxxxx> This commit adds a new flag DM_OPEN_SHARED. The flag may be used on the create ioctl. When it is used, the underlying devices that are opened will be open in a shareable mode, so that the user can mount filesystems on them or perform other activity. Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx> --- drivers/md/dm-core.h | 1 + drivers/md/dm-ioctl.c | 4 ++-- drivers/md/dm.c | 9 +++++++-- include/linux/device-mapper.h | 2 +- include/uapi/linux/dm-ioctl.h | 6 ++++++ 5 files changed, 17 insertions(+), 5 deletions(-) Index: linux-2.6/drivers/md/dm-core.h =================================================================== --- linux-2.6.orig/drivers/md/dm-core.h 2024-07-30 14:06:48.000000000 +0200 +++ linux-2.6/drivers/md/dm-core.h 2024-11-11 17:34:13.000000000 +0100 @@ -161,6 +161,7 @@ struct mapped_device { #define DMF_SUSPENDED_INTERNALLY 7 #define DMF_POST_SUSPENDING 8 #define DMF_EMULATE_ZONE_APPEND 9 +#define DMF_OPEN_SHARED 10 void disable_discard(struct mapped_device *md); void disable_write_zeroes(struct mapped_device *md); Index: linux-2.6/drivers/md/dm-ioctl.c =================================================================== --- linux-2.6.orig/drivers/md/dm-ioctl.c 2024-09-02 17:35:39.000000000 +0200 +++ linux-2.6/drivers/md/dm-ioctl.c 2024-11-11 17:35:51.000000000 +0100 @@ -888,7 +888,7 @@ static int dev_create(struct file *filp, if (param->flags & DM_PERSISTENT_DEV_FLAG) m = MINOR(huge_decode_dev(param->dev)); - r = dm_create(m, &md); + r = dm_create(m, param->flags, &md); if (r) return r; @@ -2283,7 +2283,7 @@ int __init dm_early_create(struct dm_ioc m = MINOR(huge_decode_dev(dmi->dev)); /* alloc dm device */ - r = dm_create(m, &md); + r = dm_create(m, 0, &md); if (r) return r; Index: linux-2.6/drivers/md/dm.c =================================================================== --- linux-2.6.orig/drivers/md/dm.c 2024-11-07 12:49:13.000000000 +0100 +++ linux-2.6/drivers/md/dm.c 2024-11-11 17:35:05.000000000 +0100 @@ -737,7 +737,9 @@ static struct table_device *open_table_d return ERR_PTR(-ENOMEM); refcount_set(&td->count, 1); - bdev_file = bdev_file_open_by_dev(dev, mode, _dm_claim_ptr, NULL); + bdev_file = bdev_file_open_by_dev(dev, mode, + test_bit(DMF_OPEN_SHARED, &md->flags) ? NULL :_dm_claim_ptr, + NULL); if (IS_ERR(bdev_file)) { r = PTR_ERR(bdev_file); goto out_free_td; @@ -2489,7 +2491,7 @@ static struct dm_table *__unbind(struct /* * Constructor for a new device. */ -int dm_create(int minor, struct mapped_device **result) +int dm_create(int minor, uint32_t flags, struct mapped_device **result) { struct mapped_device *md; @@ -2497,6 +2499,9 @@ int dm_create(int minor, struct mapped_d if (!md) return -ENXIO; + if (flags & DM_OPEN_SHARED) + set_bit(DMF_OPEN_SHARED, &md->flags); + dm_ima_reset_data(md); *result = md; Index: linux-2.6/include/linux/device-mapper.h =================================================================== --- linux-2.6.orig/include/linux/device-mapper.h 2024-10-16 16:41:33.000000000 +0200 +++ linux-2.6/include/linux/device-mapper.h 2024-11-11 17:31:32.000000000 +0100 @@ -483,7 +483,7 @@ void dm_consume_args(struct dm_arg_set * * DM_ANY_MINOR chooses the next available minor number. */ #define DM_ANY_MINOR (-1) -int dm_create(int minor, struct mapped_device **md); +int dm_create(int minor, uint32_t flags, struct mapped_device **md); /* * Reference counting for md. Index: linux-2.6/include/uapi/linux/dm-ioctl.h =================================================================== --- linux-2.6.orig/include/uapi/linux/dm-ioctl.h 2023-09-05 14:46:02.000000000 +0200 +++ linux-2.6/include/uapi/linux/dm-ioctl.h 2024-11-11 17:33:33.000000000 +0100 @@ -382,4 +382,10 @@ enum { */ #define DM_IMA_MEASUREMENT_FLAG (1 << 19) /* In */ +/* + * Open underlying devices in the shareable mode, so that the user can mount + * filesystems on them. + */ +#define DM_OPEN_SHARED (1 << 20) /* In */ + #endif /* _LINUX_DM_IOCTL_H */
