[CRIU] [PATCH] link_remap: do not create excessive links for a single file

[Pavel Emelyanov]

On 07/13/2016 04:10 PM, Stanislav Kinsburskiy wrote:
> 
> 
> 13.07.2016 14:48, Pavel Emelyanov пишет:
>> On 06/30/2016 08:11 PM, Stanislav Kinsburskiy wrote:
>>> Currently criu always creates link for each file, considered as "silly-renamed".
>>> Even in those cases, when file is opened multiple times, it creates one new
>>> link for each occurrence.
>>> On restore only one link file is used for all the file descriptors, sharing
>>> this path. And only this link is removed.
>> Would you cook a zdtm test showing it?
> 
> Sorry, I don't understand. Showing what exactly?
> I caught by using zdtm tests. Test "static/unlink_mmap00" should expose it.
> Two links created, only one used and unlinked. Another one stays on the 
> disk.

And test passes :) Then modify it (or it's cleanup hook) to catch this error.

>>> The rest of the links are forgotten and abandoned on file system.
>>> This patch fixed this mess by creating the link only iff it's unique. Or
>>> skipping this job otherwise.
>>>
>>> Signed-off-by: Stanislav Kinsburskiy <skinsbursky at virtuozzo.com>
>>> ---
>>>   criu/files-reg.c |   50 ++++++++++++++++++++++++++++++++++++++++++++------
>>>   1 file changed, 44 insertions(+), 6 deletions(-)
>>>
>>> diff --git a/criu/files-reg.c b/criu/files-reg.c
>>> index fd36ae9..b1ad271 100644
>>> --- a/criu/files-reg.c
>>> +++ b/criu/files-reg.c
>>> @@ -70,9 +70,11 @@ struct link_remap_rlb {
>>>   	struct list_head	list;
>>>   	struct ns_id		*mnt_ns;
>>>   	char			*path;
>>> +	char			*orig;
>>> +	u32			id;
>>>   };
>>>   
>>> -static int note_link_remap(char *path, struct ns_id *nsid)
>>> +static int note_link_remap(char *path, char *orig, struct ns_id *nsid, u32 id)
>>>   {
>>>   	struct link_remap_rlb *rlb;
>>>   
>>> @@ -84,11 +86,18 @@ static int note_link_remap(char *path, struct ns_id *nsid)
>>>   	if (!rlb->path)
>>>   		goto err2;
>>>   
>>> +	rlb->orig = strdup(orig);
>>> +	if (!rlb->orig)
>>> +		goto err3;
>>> +
>>>   	rlb->mnt_ns = nsid;
>>> +	rlb->id = id;
>>>   	list_add(&rlb->list, &remaps);
>>>   
>>>   	return 0;
>>>   
>>> +err3:
>>> +	xfree(rlb->path);
>>>   err2:
>>>   	xfree(rlb);
>>>   err:
>>> @@ -96,6 +105,22 @@ err:
>>>   	return -1;
>>>   }
>>>   
>>> +static int find_link_remap(char *path, struct ns_id *nsid, u32 *id)
>>> +{
>>> +	struct link_remap_rlb *rlb;
>>> +
>>> +	list_for_each_entry(rlb, &remaps, list) {
>>> +		if (rlb->mnt_ns != nsid)
>>> +			continue;
>>> +		if (strcmp(rlb->orig, path))
>>> +			continue;
>>> +
>>> +		*id = rlb->id;
>>> +		return 0;
>>> +	}
>>> +	return -ENOENT;
>>> +}
>>> +
>>>   /* Trim "a/b/c/d" to "a/b/d" */
>>>   static int trim_last_parent(char *path)
>>>   {
>>> @@ -725,6 +750,7 @@ static void __rollback_link_remaps(bool do_unlink)
>>>   		}
>>>   
>>>   		list_del(&rlb->list);
>>> +		xfree(rlb->orig);
>>>   		xfree(rlb->path);
>>>   		xfree(rlb);
>>>   	}
>>> @@ -781,28 +807,40 @@ static int create_link_remap(char *path, int len, int lfd,
>>>   		return -1;
>>>   	}
>>>   
>>> -	if (note_link_remap(link_name, nsid))
>>> +	if (note_link_remap(link_name, path, nsid, *idp))
>>>   		return -1;
>>>   
>>>   	return pb_write_one(img_from_set(glob_imgset, CR_FD_REG_FILES), &rfe, PB_REG_FILE);
>>>   }
>>>   
>>> -static int dump_linked_remap(char *path, int len, const struct stat *ost,
>>> -				int lfd, u32 id, struct ns_id *nsid)
>>> +static int dump_linked_remap_type(char *path, int len, int lfd, u32 id, struct ns_id *nsid, RemapType remap_type, bool unique)
>>>   {
>>>   	u32 lid;
>>>   	RemapFilePathEntry rpe = REMAP_FILE_PATH_ENTRY__INIT;
>>>   
>>> -	if (create_link_remap(path, len, lfd, &lid, nsid))
>>> -		return -1;
>>> +	if (!find_link_remap(path, nsid, &lid)) {
>>> +		pr_debug("Link remap for %s already exists with id %x\n",
>>> +				path, lid);
>>> +		if (unique)
>>> +			return 0;
>>> +	} else if (create_link_remap(path, len, lfd, &lid, nsid))
>>> +			return -1;
>>>   
>>>   	rpe.orig_id = id;
>>>   	rpe.remap_id = lid;
>>> +	rpe.has_remap_type = true;
>>> +	rpe.remap_type = remap_type;
>>>   
>>>   	return pb_write_one(img_from_set(glob_imgset, CR_FD_REMAP_FPATH),
>>>   			&rpe, PB_REMAP_FPATH);
>>>   }
>>>   
>>> +static int dump_linked_remap(char *path, int len, const struct stat *ost,
>>> +				int lfd, u32 id, struct ns_id *nsid)
>>> +{
>>> +	return dump_linked_remap_type(path, len, lfd, id, nsid, REMAP_TYPE__LINKED, false);
>>> +}
>>> +
>>>   static pid_t *dead_pids;
>>>   static int n_dead_pids;
>>>   
>>>
>>> _______________________________________________
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>>> CRIU at openvz.org
>>> https://lists.openvz.org/mailman/listinfo/criu
>>> .
>>>
> 
> .
>