[Devel] [PATCH rhel6 2/3] cpt: dump dentry alias path for UNIX socket

[Stanislav Kinsburskiy]

28.09.2015 17:57, Vasily Averin пишет:
> Stas,
> please see my comment below.
>
> On 28.09.2015 16:16, Stanislav Kinsburskiy wrote:
>> From: Stanislav Kinsburskiy <skinsbursky at parallels.com>
>>
>> There could be a unix socket (thanks to supervisord), which was unlinked, but
>> also a hardlink to it was created prior to unlink.
>> This basically means, that unlinked socket and it's hardlink points to the
>> same inode.
>> In such a case we can't just recreate unlinked socket in /tmp directory, like
>> we did before. Becuase it this case connect to linked dentry will fail becuase
>> of different inode.
>> We have to try to find another dentry, poiting to this inode and dump it's
>> path, which will be used to recreate unlinked socket on restore.
>> We need also to dump dentry mount, so we can lookup it on restore. BTW, in
>> this case socket will be restored via unix_bind_to_mntref() instead of
>> unix_bind_to_path().
>>
>> Signed-off-by: Stanislav Kinsburskiy <skinsbursky at parallels.com>
>> ---
>>   include/linux/cpt_image.h |    5 ++++
>>   kernel/cpt/cpt_socket.c   |   52 +++++++++++++++++++++++++++++++--------------
>>   2 files changed, 41 insertions(+), 16 deletions(-)
>>
>> diff --git a/include/linux/cpt_image.h b/include/linux/cpt_image.h
>> index 30a625d..75fa878 100644
>> --- a/include/linux/cpt_image.h
>> +++ b/include/linux/cpt_image.h
>> @@ -963,6 +963,11 @@ struct cpt_sock_image
>>   
>>   	__u32	cpt_i_uid;
>>   	__u32	cpt_i_gid;
>> +
>> +	__u32	cpt_d_alias[128/4];
>> +
>> +	__u32	cpt_d_aliaslen;
>> +	__u32	__cpt_pad15;
>>   } __attribute__ ((aligned (8)));
> size of this structure increases ==> CPT image version should be increased ==> it's impossible to migrate from new kernels to old ones.
> Am I missed something?

Frankly, yes.
It's not necessary to change image version.
There is a "cpd_object_has()" helper, allowing to check, whether image 
has additional fields at the end or not dynamically. IOW, old kernel 
won't notice these new fields and will proceed as before.
It's used in third patch of the series.

>
>>   struct cpt_sockmc_image {
>> diff --git a/kernel/cpt/cpt_socket.c b/kernel/cpt/cpt_socket.c
>> index 863aefe..88b4bd7 100644
>> --- a/kernel/cpt/cpt_socket.c
>> +++ b/kernel/cpt/cpt_socket.c
>> @@ -543,28 +543,47 @@ static int cpt_dump_unix_socket(struct sock *sk, struct cpt_sock_image *v, cpt_c
>>   
>>   	if (unix_sk(sk)->dentry) {
>>   		struct dentry *d = unix_sk(sk)->dentry;
>> +		unsigned long pg = __get_free_page(GFP_KERNEL);
>> +		struct path p;
>> +		char *path, *cpt_path;
>> +		int err = 0;
>> +		__u32 *path_len;
>> +
>> +		if (!pg)
>> +			return -ENOMEM;
>> +
>>   		v->cpt_i_uid = d->d_inode->i_uid;
>>   		v->cpt_i_gid = d->d_inode->i_gid;
>>   
>>   		if (IS_ROOT(d) || !d_unhashed(d)) {
>> -			int err = 0;
>> -			struct path p = {unix_sk(sk)->mnt, d};
>> -			char *path;
>> -			unsigned long pg = __get_free_page(GFP_KERNEL);
>> +			p.dentry = dget(d);
>> +			cpt_path = ((char*)v->cpt_laddr) + 2;
>> +			path_len = &v->cpt_laddrlen;
>> +		} else {
>> +			v->cpt_sockflags |= CPT_SOCK_DELETED;
>> +			v->cpt_d_aliaslen = 0;
>> +			p.dentry = NULL;
>>   
>> -			if (!pg)
>> -				return -ENOMEM;
>> +			if (d->d_inode->i_nlink != 0) {
>> +				p.dentry = get_linked_dentry(d, unix_sk(sk)->mnt, ctx);
>> +				cpt_path = (char *)v->cpt_d_alias;
>> +				path_len = &v->cpt_d_aliaslen;
>> +			}
>> +		}
>> +
>> +		if (!IS_ERR_OR_NULL(p.dentry)) {
>> +			p.mnt = unix_sk(sk)->mnt;
>>   
>>   			path = d_path(&p, (char *)pg, PAGE_SIZE);
>>   
>>   			if (!IS_ERR(path)) {
>>   				int len = strlen(path);
>>   				if (len < 126) {
>> -					strcpy(((char*)v->cpt_laddr)+2, path);
>> -					v->cpt_laddrlen = len + 2;
>> -				} else {
>> -					wprintk_ctx("af_unix path is too long: %s (%s)\n", path, ((char*)v->cpt_laddr)+2);
>> -				}
>> +					strcpy(cpt_path, path);
>> +					*path_len = len + 2;
>> +				} else
>> +					wprintk_ctx("af_unix path is too long: %s (%s)\n", path, cpt_path);
>> +
>>   				if (cpt_need_delayfs(unix_sk(sk)->mnt))
>>   					v->cpt_sockflags |= CPT_SOCK_DELAYED;
>>   
>> @@ -575,11 +594,12 @@ static int cpt_dump_unix_socket(struct sock *sk, struct cpt_sock_image *v, cpt_c
>>   				eprintk_ctx("cannot get path of an af_unix socket\n");
>>   				err = PTR_ERR(path);
>>   			}
>> -			free_page(pg);
>> -			if (err)
>> -				return err;
>> -		} else
>> -			v->cpt_sockflags |= CPT_SOCK_DELETED;
>> +			dput(p.dentry);
>> +		}
>> +
>> +		free_page(pg);
>> +		if (err)
>> +			return err;
>>   	}
>>   
>>   	/* If the socket is connected, find its peer. If peer is not
>>
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