On Mon, Nov 21, 2022 at 03:28:52PM +0100, Lukas Czerner wrote:
> In memory quota format relies on quota infrastructure to store dquot
> information for us. While conventional quota formats for file systems
> with persistent storage can load quota information into dquot from the
> storage on-demand and hence quota dquot shrinker can free any dquot that
> is not currently being used, it must be avoided here. Otherwise we can
> lose valuable information, user provided limits, because there is no
> persistent storage to load the information from afterwards.
>
> One information that in-memory quota format needs to keep track of is a
> sorted list of ids for each quota type. This is done by utilizing an rb
> tree which root is stored in mem_dqinfo->dqi_priv for each quota type.
>
> This format can be used to support quota on file system without persistent
> storage such as tmpfs.
>
> Signed-off-by: Lukas Czerner <lczerner@xxxxxxxxxx>
> ---
> fs/quota/Kconfig | 8 ++
> fs/quota/Makefile | 1 +
> fs/quota/dquot.c | 3 +
> fs/quota/quota_mem.c | 260 +++++++++++++++++++++++++++++++++++++
> include/linux/quota.h | 7 +-
> include/uapi/linux/quota.h | 1 +
> 6 files changed, 279 insertions(+), 1 deletion(-)
> create mode 100644 fs/quota/quota_mem.c
>
> diff --git a/fs/quota/Kconfig b/fs/quota/Kconfig
> index b59cd172b5f9..8ea9656ca37b 100644
> --- a/fs/quota/Kconfig
> +++ b/fs/quota/Kconfig
> @@ -67,6 +67,14 @@ config QFMT_V2
> also supports 64-bit inode and block quota limits. If you need this
> functionality say Y here.
>
> +config QFMT_MEM
> + tristate "Quota in-memory format support "
> + depends on QUOTA
> + help
> + This config option enables kernel support for in-memory quota
> + format support. Useful to support quota on file system without
> + permanent storage. If you need this functionality say Y here.
> +
> config QUOTACTL
> bool
> default n
> diff --git a/fs/quota/Makefile b/fs/quota/Makefile
> index 9160639daffa..935be3f7b731 100644
> --- a/fs/quota/Makefile
> +++ b/fs/quota/Makefile
> @@ -5,3 +5,4 @@ obj-$(CONFIG_QFMT_V2) += quota_v2.o
> obj-$(CONFIG_QUOTA_TREE) += quota_tree.o
> obj-$(CONFIG_QUOTACTL) += quota.o kqid.o
> obj-$(CONFIG_QUOTA_NETLINK_INTERFACE) += netlink.o
> +obj-$(CONFIG_QFMT_MEM) += quota_mem.o
> diff --git a/fs/quota/dquot.c b/fs/quota/dquot.c
> index 0427b44bfee5..f1a7a03632a2 100644
> --- a/fs/quota/dquot.c
> +++ b/fs/quota/dquot.c
> @@ -736,6 +736,9 @@ dqcache_shrink_scan(struct shrinker *shrink, struct shrink_control *sc)
> spin_lock(&dq_list_lock);
> while (!list_empty(&free_dquots) && sc->nr_to_scan) {
> dquot = list_first_entry(&free_dquots, struct dquot, dq_free);
> + if (test_bit(DQ_NO_SHRINK_B, &dquot->dq_flags) &&
> + !test_bit(DQ_FAKE_B, &dquot->dq_flags))
> + continue;
> remove_dquot_hash(dquot);
> remove_free_dquot(dquot);
> remove_inuse(dquot);
> diff --git a/fs/quota/quota_mem.c b/fs/quota/quota_mem.c
> new file mode 100644
> index 000000000000..7d5e82122143
> --- /dev/null
> +++ b/fs/quota/quota_mem.c
> @@ -0,0 +1,260 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * In memory quota format relies on quota infrastructure to store dquot
> + * information for us. While conventional quota formats for file systems
> + * with persistent storage can load quota information into dquot from the
> + * storage on-demand and hence quota dquot shrinker can free any dquot
> + * that is not currently being used, it must be avoided here. Otherwise we
> + * can lose valuable information, user provided limits, because there is
> + * no persistent storage to load the information from afterwards.
> + *
> + * One information that in-memory quota format needs to keep track of is
> + * a sorted list of ids for each quota type. This is done by utilizing
> + * an rb tree which root is stored in mem_dqinfo->dqi_priv for each quota
> + * type.
> + *
> + * This format can be used to support quota on file system without persistent
> + * storage such as tmpfs.
> + */
> +#include <linux/errno.h>
> +#include <linux/fs.h>
> +#include <linux/mount.h>
> +#include <linux/kernel.h>
> +#include <linux/init.h>
> +#include <linux/module.h>
> +#include <linux/slab.h>
> +#include <linux/rbtree.h>
> +
> +#include <linux/quotaops.h>
> +#include <linux/quota.h>
> +
> +MODULE_AUTHOR("Lukas Czerner");
> +MODULE_DESCRIPTION("Quota in-memory format support");
> +MODULE_LICENSE("GPL");
> +
> +/*
> + * The following constants define the amount of time given a user
> + * before the soft limits are treated as hard limits (usually resulting
> + * in an allocation failure). The timer is started when the user crosses
> + * their soft limit, it is reset when they go below their soft limit.
> + */
> +#define MAX_IQ_TIME 604800 /* (7*24*60*60) 1 week */
> +#define MAX_DQ_TIME 604800 /* (7*24*60*60) 1 week */
> +
> +struct quota_id {
> + struct rb_node node;
> + qid_t id;
> +};
> +
> +static int mem_check_quota_file(struct super_block *sb, int type)
> +{
> + /* There is no real quota file, nothing to do */
> + return 1;
> +}
> +
> +/*
> + * There is no real quota file. Just allocate rb_root for quota ids and
> + * set limits
> + */
> +static int mem_read_file_info(struct super_block *sb, int type)
> +{
> + struct quota_info *dqopt = sb_dqopt(sb);
> + struct mem_dqinfo *info = &dqopt->info[type];
> + int ret = 0;
> +
> + down_read(&dqopt->dqio_sem);
> + if (info->dqi_fmt_id != QFMT_MEM_ONLY) {
> + ret = -EINVAL;
> + goto out_unlock;
> + }
> +
> + info->dqi_priv = kzalloc(sizeof(struct rb_root), GFP_NOFS);
> + if (!info->dqi_priv) {
> + ret = -ENOMEM;
> + goto out_unlock;
> + }
> +
> + /*
> + * Used space is stored as unsigned 64-bit value in bytes but
> + * quota core supports only signed 64-bit values so use that
> + * as a limit
> + */
> + info->dqi_max_spc_limit = 0x7fffffffffffffffLL; /* 2^63-1 */
> + info->dqi_max_ino_limit = 0x7fffffffffffffffLL;
> +
> + info->dqi_bgrace = MAX_DQ_TIME;
> + info->dqi_igrace = MAX_IQ_TIME;
> + info->dqi_flags = 0;
> +
> +out_unlock:
> + up_read(&dqopt->dqio_sem);
> + return ret;
> +}
> +
> +static int mem_write_file_info(struct super_block *sb, int type)
> +{
> + /* There is no real quota file, nothing to do */
> + return 0;
> +}
> +
> +/*
> + * Free all the quota_id entries in the rb tree and rb_root.
> + */
> +static int mem_free_file_info(struct super_block *sb, int type)
> +{
> + struct mem_dqinfo *info = &sb_dqopt(sb)->info[type];
> + struct rb_root *root = info->dqi_priv;
> + struct quota_id *entry;
> + struct rb_node *node;
> +
> + info->dqi_priv = NULL;
> + node = rb_first(root);
> + while (node) {
> + entry = rb_entry(node, struct quota_id, node);
> + node = rb_next(&entry->node);
> +
> + rb_erase(&entry->node, root);
> + kfree(entry);
> + }
> +
> + kfree(root);
> + return 0;
> +}
> +
> +/*
> + * There is no real quota file, nothing to read. Just insert the id in
> + * the rb tree.
> + */
> +static int mem_read_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 rb_node *parent = NULL, *new_node = NULL;
> + struct quota_id *new_entry, *entry;
> + qid_t id = from_kqid(&init_user_ns, dquot->dq_id);
Hey Lukas,
tmpfs instances can be mounted inside of mount namespaces owned by user
namespaces as is the case in unprivileged containers. An easy example is:
unshare --mount --user --map-root
mount -t tmpfs tmpfs /mnt
This tmpfs instances will be mounted with sb->s_user_ns set to the
userns just created during the unshare call and not to init_user_ns. So
this means that the filesystem idmapping isn't a 1:1 mapping. This needs
to be taken into account:
qid_t id = from_kqid(sb->s_user_ns, dquot->dq_id);
similar below.
But dquot_load_quota_sb() which you use in a later patch is restricted
to the init_user_ns which means that your patch as it stands is only
useable for tmpfs instances mounted in the init_user_ns.
If that's intentional then the code above is probably fine but if it's
not then you need preliminary patches to support quotas from filesystems
mountable in non-initial user namespaces.
Enabling this shouldn't be a big deal as it mostly involves updating
callsites to account for sb->s_user_ns when reading and writing quotas.
I've looked at that a while ago but there was no filesystem with quota
support that was also mountable in a user namespaces. Idmapped mounts
are already taken care of.
