From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:51997) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1gWHyN-0000yO-2m for qemu-devel@nongnu.org; Mon, 10 Dec 2018 04:35:32 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1gWHyJ-0007zG-O3 for qemu-devel@nongnu.org; Mon, 10 Dec 2018 04:35:30 -0500 From: Paul Durrant Date: Mon, 10 Dec 2018 09:35:00 +0000 Message-ID: <61b61d8f7ebc41bc9ed06fc21616160f@AMSPEX02CL03.citrite.net> References: <1544108924-10841-1-git-send-email-paul.durrant@citrix.com> <1544108924-10841-4-git-send-email-paul.durrant@citrix.com> <20181207143525.GF18875@perard.uk.xensource.com> <20181207152601.GH18875@perard.uk.xensource.com> In-Reply-To: <20181207152601.GH18875@perard.uk.xensource.com> Content-Language: en-US Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Subject: Re: [Qemu-devel] [PATCH v2 03/18] xen: introduce 'xen-block', 'xen-disk' and 'xen-cdrom' List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Anthony Perard Cc: "qemu-devel@nongnu.org" , "qemu-block@nongnu.org" , "xen-devel@lists.xenproject.org" , Kevin Wolf , Max Reitz , Stefano Stabellini > -----Original Message----- > From: Anthony PERARD [mailto:anthony.perard@citrix.com] > Sent: 07 December 2018 15:26 > To: Paul Durrant > Cc: qemu-devel@nongnu.org; qemu-block@nongnu.org; xen- > devel@lists.xenproject.org; Kevin Wolf ; Max Reitz > ; Stefano Stabellini > Subject: Re: [PATCH v2 03/18] xen: introduce 'xen-block', 'xen-disk' and > 'xen-cdrom' >=20 > On Fri, Dec 07, 2018 at 02:39:40PM +0000, Paul Durrant wrote: > > > -----Original Message----- > > > From: Anthony PERARD [mailto:anthony.perard@citrix.com] > > > Sent: 07 December 2018 14:35 > > > To: Paul Durrant > > > Cc: qemu-devel@nongnu.org; qemu-block@nongnu.org; xen- > > > devel@lists.xenproject.org; Kevin Wolf ; Max Reitz > > > ; Stefano Stabellini > > > Subject: Re: [PATCH v2 03/18] xen: introduce 'xen-block', 'xen-disk' > and > > > 'xen-cdrom' > > > > > > On Thu, Dec 06, 2018 at 03:08:29PM +0000, Paul Durrant wrote: > > > > +static char *disk_to_vbd_name(unsigned int disk) > > > > +{ > > > > + char *name, *prefix =3D (disk >=3D 26) ? > > > > + disk_to_vbd_name((disk / 26) - 1) : g_strdup(""); > > > > + > > > > + name =3D g_strdup_printf("%s%c", prefix, 'a' + disk); > > > > > > I don't think that works, if disk is 27, we do ('a' + 27) here. It's > > > probably missing a `disk % 26`. > > > > Damn, yes I was not allowing the >2 letters. > > > > > > > > > + g_free(prefix); > > > > + > > > > + return name; > > > > +} > > > > > > [...] > > > > > > > +static unsigned int vbd_name_to_disk(const char *name, const char > > > **endp) > > > > +{ > > > > + unsigned int disk =3D 0; > > > > + > > > > + while (*name !=3D '\0') { > > > > + if (!g_ascii_isalpha(*name) || !g_ascii_islower(*name)) { > > > > + break; > > > > + } > > > > + > > > > + disk *=3D 26; > > > > + disk +=3D *name++ - 'a'; > > > > + } > > > > + *endp =3D name; > > > > + > > > > + return disk; > > > > +} > > > > + > > > > +static void xen_block_set_vdev(Object *obj, Visitor *v, const char > > > *name, > > > > + void *opaque, Error **errp) > > > > +{ > > > > > > Setting vdev doesn't work. I've tried to add a disk `xvdaa', and it > > > result in `xvda', or `d0p0' (in the trace). (Same result with > `xvdaaa', > > > and 'xvdba' gives 'xvdaa'/d26p0) > > > > > > > Ok, that's weird. I'll have to figure that out. >=20 > It's probably because 'a' is somtime 0 and sometime is 1. >=20 > 'a' should be 0 > 'aa' should be 26, > 'aaa' Seems to be 702. >=20 > 'xvda': 0 -> 0 * 1 > 'xvdz': 25 -> 25 * 1 > 'xvdaa': 26 -> 1 * 26 + 0 * 1 > 'xvdaaa': 702 -> 1 * 26^2 + 1 * 26 + 0 * 1 >=20 > So, it's weird. Have fun fixing the algorithm for that. Actually not as hard as it seemed at first... just treat 'a' as 1 while acc= umulating the number and then subtract 1 from the result. I wrote a tool to= generate the first N disk names using a simple "overflow 'z' to 'aa'" (i.e= . non-arithmetical) rule to check against and it matches all the cases I tr= ied (up to 4 letters). Paul >=20 > -- > Anthony PERARD