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

[Carlos Maiolino <cem@kernel.org>]

On Thu, Apr 20, 2023 at 04:39:54PM +0200, Jan Kara wrote:
> 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
> 
Thanks!

> > @@ -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.

Hmmm, I think I see what you mean. I can make usrquota_block_hardlimit options
to not actually set the quota flag on quota_types, so this should be explicitly
set by usrquota/grpquota options. Does that work for you?

> 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.
> 

hmm, yes, maybe enabling default limits to be changed on remount isn't a big
deal, once the quota is already enabled, so everything is already in place.

> > 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?

hmmm, which struct are you talking about? quota_id? As we do for DQ_FAKE?


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

-- 
Carlos Maiolino