Re: [PATCH 6/6] Add default quota limit mount options

[Jan Kara <jack@suse.cz>]

On Thu 20-04-23 10:03:59, cem@kernel.org wrote:
> From: Lukas Czerner <lczerner@redhat.com>
> 
> Allow system administrator to set default global quota limits at tmpfs
> mount time.
> 
> Signed-off-by: Lukas Czerner <lczerner@redhat.com>
> Signed-off-by: Carlos Maiolino <cmaiolino@redhat.com>
> ---
>  Documentation/filesystems/tmpfs.rst | 34 ++++++++++----
>  include/linux/shmem_fs.h            |  8 ++++
>  mm/shmem.c                          | 69 +++++++++++++++++++++++++++++
>  mm/shmem_quota.c                    |  9 ++++
>  4 files changed, 111 insertions(+), 9 deletions(-)
> 
> diff --git a/Documentation/filesystems/tmpfs.rst b/Documentation/filesystems/tmpfs.rst
> index 1d4ef4f7cca7e..241c11f86cd73 100644
> --- a/Documentation/filesystems/tmpfs.rst
> +++ b/Documentation/filesystems/tmpfs.rst
> @@ -88,15 +88,31 @@ that instance in a system with many CPUs making intensive use of it.
>  
>  tmpfs also supports quota with the following mount options
>  
> -========  =============================================================
> -quota     User and group quota accounting and enforcement is enabled on
> -          the mount. Tmpfs is using hidden system quota files that are
> -          initialized on mount.
> -usrquota  User quota accounting and enforcement is enabled on the
> -          mount.
> -grpquota  Group quota accounting and enforcement is enabled on the
> -          mount.
> -========  =============================================================
> +======================== =================================================
> +quota                    User and group quota accounting and enforcement
> +                         is enabled on the mount. Tmpfs is using hidden
> +                         system quota files that are initialized on mount.
> +usrquota                 User quota accounting and enforcement is enabled
> +                         on the mount.
> +grpquota                 Group quota accounting and enforcement is enabled
> +                         on the mount.
> +usrquota_block_hardlimit Set global user quota block hard limit.
> +usrquota_inode_hardlimit Set global user quota inode hard limit.
> +grpquota_block_hardlimit Set global group quota block hard limit.
> +grpquota_inode_hardlimit Set global group quota inode hard limit.
> +======================== =================================================
> +
> +None of the quota related mount options can be set or changed on remount.
> +
> +Quota limit parameters accept a suffix k, m or g for kilo, mega and giga
> +and can't be changed on remount. Default global quota limits are taking
> +effect for any and all user/group/project except root the first time the
> +quota entry for user/group/project id is being accessed - typically the
> +first time an inode with a particular id ownership is being created after
> +the mount. In other words, instead of the limits being initialized to zero,
> +they are initialized with the particular value provided with these mount
> +options. The limits can be changed for any user/group id at any time as it
									   ^^ they
> +normally can.
	    ^^^ can be
           
> @@ -3714,6 +3723,50 @@ static int shmem_parse_one(struct fs_context *fc, struct fs_parameter *param)
>  		ctx->seen |= SHMEM_SEEN_QUOTA;
>  		ctx->quota_types |= QTYPE_MASK_GRP;
>  		break;
> +	case Opt_usrquota_block_hardlimit:
> +		size = memparse(param->string, &rest);
> +		if (*rest || !size)
> +			goto bad_value;
> +		if (size > SHMEM_QUOTA_MAX_SPC_LIMIT)
> +			return invalfc(fc,
> +				       "User quota block hardlimit too large.");
> +		ctx->qlimits.usrquota_bhardlimit = size;
> +		ctx->seen |= SHMEM_SEEN_QUOTA;
> +		ctx->quota_types |= QTYPE_MASK_USR;

So if I get it right, the intention here is that if
usrquota_block_hardlimit=value option is used, it automatically enables
user quota accounting and enforcement. I guess it is logical but it is not
documented and I'd prefer to require explicit usrquota mount option to
enable accounting & enforcement - it is then e.g. easier to parse mount
options (in userspace) for finding out whether enforcement is enabled or
not. Also I can imagine we would allow changing the default limits on
remount but it isn't easy to enable quota accounting on remount etc.

> diff --git a/mm/shmem_quota.c b/mm/shmem_quota.c
> index c0b531e2ef688..3cc53f2c35e2c 100644
> --- a/mm/shmem_quota.c
> +++ b/mm/shmem_quota.c
> @@ -166,6 +166,7 @@ static int shmem_acquire_dquot(struct dquot *dquot)
>  {
>  	struct mem_dqinfo *info = sb_dqinfo(dquot->dq_sb, dquot->dq_id.type);
>  	struct rb_node **n = &((struct rb_root *)info->dqi_priv)->rb_node;
> +	struct shmem_sb_info *sbinfo = dquot->dq_sb->s_fs_info;
>  	struct rb_node *parent = NULL, *new_node = NULL;
>  	struct quota_id *new_entry, *entry;
>  	qid_t id = from_kqid(&init_user_ns, dquot->dq_id);
> @@ -195,6 +196,14 @@ static int shmem_acquire_dquot(struct dquot *dquot)
>  	}
>  
>  	new_entry->id = id;
> +	if (dquot->dq_id.type == USRQUOTA) {
> +		new_entry->bhardlimit = sbinfo->qlimits.usrquota_bhardlimit;
> +		new_entry->ihardlimit = sbinfo->qlimits.usrquota_ihardlimit;
> +	} else if (dquot->dq_id.type == GRPQUOTA) {
> +		new_entry->bhardlimit = sbinfo->qlimits.grpquota_bhardlimit;
> +		new_entry->ihardlimit = sbinfo->qlimits.grpquota_ihardlimit;
> +	}
> +
>  	new_node = &new_entry->node;
>  	rb_link_node(new_node, parent, n);
>  	rb_insert_color(new_node, (struct rb_root *)info->dqi_priv);

Maybe in shmem_dquot_release() when usage is 0 and limits are at default
limits, we can free the structure?

								Honza
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR