From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:54986) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1WxFgK-0005lZ-SP for qemu-devel@nongnu.org; Wed, 18 Jun 2014 09:13:48 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1WxFgD-0005YT-CP for qemu-devel@nongnu.org; Wed, 18 Jun 2014 09:13:40 -0400 Received: from mx1.redhat.com ([209.132.183.28]:26062) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1WxFgD-0005Xk-46 for qemu-devel@nongnu.org; Wed, 18 Jun 2014 09:13:33 -0400 Date: Wed, 18 Jun 2014 09:13:28 -0400 From: Jeff Cody Message-ID: <20140618131328.GA8856@localhost.localdomain> References: <526da734a5f3cffd2eb56accafdb4add38c75270.1403041699.git.jcody@redhat.com> <20140618125315.GA4107@irqsave.net> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline In-Reply-To: <20140618125315.GA4107@irqsave.net> Content-Transfer-Encoding: quoted-printable Subject: Re: [Qemu-devel] [PATCH v6 for 2.1 01/10] block: Auto-generate node_names for each BDS entry List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: =?iso-8859-1?Q?Beno=EEt?= Canet Cc: kwolf@redhat.com, pkrempa@redhat.com, famz@redhat.com, qemu-devel@nongnu.org, stefanha@redhat.com On Wed, Jun 18, 2014 at 02:53:15PM +0200, Beno=EEt Canet wrote: > The Tuesday 17 Jun 2014 =E0 17:53:49 (-0400), Jeff Cody wrote : > > Currently, node_name is only filled in when done so explicitly by the > > user. If no node_name is specified, then the node name field is not > > populated. > >=20 > > If node_names are automatically generated when not specified, that me= ans > > that all block job operations can be done by reference to the unique > > node_name field. This eliminates ambiguity in resolving filenames > > (relative filenames, or file descriptors, symlinks, mounts, etc..) th= at > > qemu currently needs to deal with. > >=20 > > If a node name is specified, then it will not be automatically > > generated for that BDS entry. > >=20 > > If it is automatically generated, it will be prefaced with "__qemu##"= , > > followed by 8 characters of a unique number, followed by 8 random > > ASCII characters in the range of 'A-Z'. Some sample generated node-n= ame > > strings: > > __qemu##00000000IAIYNXXR > > __qemu##00000002METXTRBQ > > __qemu##00000001FMBORDWG >=20 > Jeff can't we simply enforce the namespace separation with a check on t= he QDict > option content ? > This way we could be sure that the user can't input a node-name startin= g with > __qemu. > That still would not stop a user from trying to 'predict' or assuming what a node name would be ("oh, it is the first drive, it is probably __qemu##0000", etc...). Having the combination of the incrementing counter and the random string generation guarantees 2 things: it will always be unique in a qemu session, and it is not predictable by the user. The "__qemu##" just helps to visually identify it as a qemu generated. Although if you are strictly concerned about namespace confusion, we could enforce the namespace as you suggest, so a user could not create a node-name that would look like a qemu-generated node-name. Even in that case, I would still want to keep the sequential number + random string. > >=20 > > The prefix is to aid in identifying it as a qemu-generated name, the > > numeric portion is to guarantee uniqueness in a given qemu session, a= nd > > the random characters are to further avoid any accidental collisions > > with user-specified node-names. > >=20 > > Reviewed-by: Eric Blake > > Signed-off-by: Jeff Cody > > --- > > block.c | 16 +++++++++++++++- > > 1 file changed, 15 insertions(+), 1 deletion(-) > >=20 > > diff --git a/block.c b/block.c > > index 43abe96..da32bb0 100644 > > --- a/block.c > > +++ b/block.c > > @@ -843,12 +843,26 @@ static int bdrv_open_flags(BlockDriverState *bs= , int flags) > > return open_flags; > > } > > =20 > > +#define GEN_NODE_NAME_PREFIX "__qemu##" > > +#define GEN_NODE_NAME_MAX_LEN (sizeof(GEN_NODE_NAME_PREFIX) + 8 + = 8) > > static void bdrv_assign_node_name(BlockDriverState *bs, > > const char *node_name, > > Error **errp) > > { > > + char gen_node_name[GEN_NODE_NAME_MAX_LEN]; > > + static uint32_t counter; /* simple counter to guarantee uniquene= ss */ > > + > > + /* if node_name is NULL, auto-generate a node name */ > > if (!node_name) { > > - return; > > + int len; > > + snprintf(gen_node_name, GEN_NODE_NAME_MAX_LEN, > > + "%s%08x", GEN_NODE_NAME_PREFIX, counter++); > > + len =3D strlen(gen_node_name); > > + while (len < GEN_NODE_NAME_MAX_LEN - 1) { > > + gen_node_name[len++] =3D g_random_int_range('A', 'Z'); > > + } > > + gen_node_name[GEN_NODE_NAME_MAX_LEN - 1] =3D '\0'; > > + node_name =3D gen_node_name; > > } > > =20 > > /* empty string node name is invalid */ > > --=20 > > 1.9.3 > >=20