[Devel] [PATCH RH7] ipc: add export_operations to mqueue sb

[Pavel Tikhomirov]

Looks good.

Reviewed-by: Pavel Tikhomirov <ptikhomirov at virtuozzo.com>

But please also see two non-critical questions below.

On 9/8/20 5:33 PM, Andrey Zhadchenko wrote:
> criu uses fhandle from fdinfo to dump inotify objects, but mqueue has no
> export_operations in super block. However, they are needed if we want to
> operate with files using fhandles.
> Add hash table as a storage for exported inodes.
> 
> https://jira.sw.ru/browse/PSBM-103727
> Signed-off-by: Andrey Zhadchenko <andrey.zhadchenko at virtuozzo.com>
> ---
>   ipc/mqueue.c | 150 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>   1 file changed, 150 insertions(+)
> 
> diff --git a/ipc/mqueue.c b/ipc/mqueue.c
> index 458e655..48ec6f8 100644
> --- a/ipc/mqueue.c
> +++ b/ipc/mqueue.c
> @@ -35,6 +35,8 @@
>   #include <linux/ipc_namespace.h>
>   #include <linux/user_namespace.h>
>   #include <linux/slab.h>
> +#include <linux/exportfs.h>
> +#include <linux/random.h>
>   
>   #include <net/sock.h>
>   #include "util.h"
> @@ -86,6 +88,7 @@ struct mqueue_inode_info {
>   };
>   
>   static const struct inode_operations mqueue_dir_inode_operations;
> +static const struct export_operations mqueue_export_ops;
>   static const struct file_operations mqueue_file_operations;
>   static const struct super_operations mqueue_super_ops;
>   static void remove_notification(struct mqueue_inode_info *info);
> @@ -117,6 +120,144 @@ static struct ipc_namespace *get_ns_from_inode(struct inode *inode)
>   	return ns;
>   }
>   
> +/*
> + * hashtable for inodes that have exported fhandles.
> + * When we export fhandle, we add it's inode into
> + * hashtable so we can find it fast
> + */
> +
> +#define MQUEUE_INODE_HASH_BITS 7

Why you've chosen smaller hash size than for cgroups?
#define CGROUP_INODE_HASH_BITS 10

> +static DEFINE_HASHTABLE(mqueue_inode_table, MQUEUE_INODE_HASH_BITS);
> +static DEFINE_SPINLOCK(mqueue_inode_table_lock);
> +
> +struct mq_inode_hitem {
> +	struct inode *inode;
> +	struct hlist_node hlist;
> +};
> +
> +static inline unsigned long mqueue_inode_get_hash(unsigned int i_ino)
> +{
> +	return hash_32(i_ino, MQUEUE_INODE_HASH_BITS);
> +}
> +
> +static struct mq_inode_hitem *mqueue_find_item_no_lock(unsigned long fh[2])
> +{
> +	struct mq_inode_hitem *i;
> +	struct hlist_head *head = mqueue_inode_table
> +		+ mqueue_inode_get_hash(fh[1]);
> +	struct mq_inode_hitem *found = NULL;
> +
> +	hlist_for_each_entry(i, head, hlist) {
> +		if (i->inode->i_generation == fh[0] &&
> +		    i->inode->i_ino == fh[1]) {
> +			found = i;
> +			break;
> +		}
> +	}
> +
> +	return found;
> +}
> +
> +static struct inode *mqueue_find_inode(unsigned long fh[2], char take_ref)
> +{
> +	struct mq_inode_hitem *item;
> +	struct inode *ret = NULL;
> +
> +	spin_lock(&mqueue_inode_table_lock);
> +	item = mqueue_find_item_no_lock(fh);
> +	if (item && take_ref && !igrab(item->inode))
> +		item = NULL;
> +	spin_unlock(&mqueue_inode_table_lock);
> +
> +	if (item)
> +		ret = item->inode;
> +
> +	return ret;
> +}
> +
> +static int mqueue_hash_add(struct inode *inode)
> +{
> +	unsigned long fh[2] = {inode->i_generation, inode->i_ino};
> +
> +	if (!mqueue_find_inode(fh, 0)) {
> +		struct mq_inode_hitem *item;
> +		struct mq_inode_hitem *existing_item = 0;
> +		struct hlist_head *head = mqueue_inode_table
> +			+ mqueue_inode_get_hash(inode->i_ino);
> +
> +		item = kmalloc(sizeof(struct mq_inode_hitem), GFP_KERNEL);
> +		if (!item)
> +			return -ENOMEM;
> +		item->inode = inode;
> +
> +		spin_lock(&mqueue_inode_table_lock);
> +		existing_item = mqueue_find_item_no_lock(fh);
> +		if (!existing_item)
> +			hlist_add_head(&item->hlist, head);
> +		spin_unlock(&mqueue_inode_table_lock);
> +
> +		if (existing_item)
> +			kfree(item);
> +	}
> +
> +	return 0;
> +}
> +
> +static void mqueue_hash_del(struct inode *inode)
> +{
> +	struct mq_inode_hitem *item;
> +	unsigned long fh[2] = {inode->i_generation, inode->i_ino};
> +
> +	spin_lock(&mqueue_inode_table_lock);
> +	item = mqueue_find_item_no_lock(fh);
> +	if (item)
> +		hlist_del(&item->hlist);
> +	spin_unlock(&mqueue_inode_table_lock);
> +
> +	kfree(item);
> +	return;
> +}
> +
> +static struct dentry *mqueue_fh_to_dentry(struct super_block *sb,
> +		struct fid *fid, int fh_len, int fh_type)
> +{
> +	struct inode *inode;
> +	struct dentry *dentry = ERR_PTR(-ENOENT);
> +	unsigned long fhandle[2] = {fid->raw[0], fid->raw[1]};
> +
> +	if (fh_len < 2)
> +		return NULL;
> +
> +	inode = mqueue_find_inode(fhandle, 1);
> +	if (inode) {
> +		dentry = d_find_alias(inode);
> +		iput(inode);
> +	}
> +	return dentry;
> +}
> +
> +static int mqueue_encode_fh(struct inode *inode, __u32 *fh, int *len,
> +				struct inode *parent)
> +{
> +	if (*len < 2) {
> +		*len = 2;
> +		return FILEID_INVALID;
> +	}
> +
> +	/*
> +	 * encode_fh is expected to return 255 (FILEID_INVALID)
> +	 * in case of failure. We can't return ENOMEM, so
> +	 * return FILEID_INVALID at least.
> +	 */
> +	if (mqueue_hash_add(inode))
> +		return FILEID_INVALID;
> +
> +	fh[0] = inode->i_generation;
> +	fh[1] = inode->i_ino;
> +	*len = 2;
> +	return 1;
> +}
> +
>   /* Auxiliary functions to manipulate messages' list */
>   static int msg_insert(struct msg_msg *msg, struct mqueue_inode_info *info)
>   {
> @@ -226,6 +367,7 @@ static struct inode *mqueue_get_inode(struct super_block *sb,
>   		goto err;
>   
>   	inode->i_ino = get_next_ino();
> +	inode->i_generation = prandom_u32();
>   	inode->i_mode = mode;
>   	inode->i_uid = current_fsuid();
>   	inode->i_gid = current_fsgid();
> @@ -316,6 +458,7 @@ static int mqueue_fill_super(struct super_block *sb, void *data, int silent)
>   	sb->s_blocksize_bits = PAGE_CACHE_SHIFT;
>   	sb->s_magic = MQUEUE_MAGIC;
>   	sb->s_op = &mqueue_super_ops;
> +	sb->s_export_op = &mqueue_export_ops;
>   
>   	inode = mqueue_get_inode(sb, ns, S_IFDIR | S_ISVTX | S_IRWXUGO, NULL);
>   	if (IS_ERR(inode))
> @@ -382,6 +525,8 @@ static void mqueue_evict_inode(struct inode *inode)
>   	if (S_ISDIR(inode->i_mode))
>   		return;
>   
> +	mqueue_hash_del(inode);
> +

Looks like for cgroups we should've also put cgroup_hash_del to 
->evict_inode helper, to be able to use igrab in cgroup_find_inode. 
Shouldn't we?

>   	ipc_ns = get_ns_from_inode(inode);
>   	info = MQUEUE_I(inode);
>   	spin_lock(&info->lock);
> @@ -1376,6 +1521,11 @@ static const struct inode_operations mqueue_dir_inode_operations = {
>   	.unlink = mqueue_unlink,
>   };
>   
> +static const struct export_operations mqueue_export_ops = {
> +	.encode_fh      = mqueue_encode_fh,
> +	.fh_to_dentry	= mqueue_fh_to_dentry,
> +};
> +
>   static const struct file_operations mqueue_file_operations = {
>   	.flush = mqueue_flush_file,
>   	.poll = mqueue_poll_file,
> 

-- 
Best regards, Tikhomirov Pavel
Software Developer, Virtuozzo.