[libvirt] [PATCH] virsh: Strip XML declaration when extracting CPU XMLs

[Jiri Denemark]

Since commit v4.3.0-336-gc84726fbdd all
{hypervisor-,}cpu-{baseline,compare} commands use a generic
vshExtractCPUDefXMLs helper for extracting individual CPU definitions
from the provided input file. The helper wraps the input file in a
<container> element so that several independent elements can be easily
parsed from the file. This works fine except when the file starts with
XML declaration (<?xml version="1.0" ... ?>) because the XML declaration
cannot be put inside any element. In fact it has to be at the very
beginning of the XML document without any preceding white space
characters. We can just simply skip the XML declaration.

https://bugzilla.redhat.com/show_bug.cgi?id=1595993

Signed-off-by: Jiri Denemark <***@redhat.com>
---
tools/virsh-host.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/tools/virsh-host.c b/tools/virsh-host.c
index 16f504bafe..b7f86bdd91 100644
--- a/tools/virsh-host.c
+++ b/tools/virsh-host.c
@@ -1130,13 +1130,20 @@ vshExtractCPUDefXMLs(vshControl *ctl,
xmlDocPtr xml = NULL;
xmlXPathContextPtr ctxt = NULL;
xmlNodePtr *nodes = NULL;
+ char *doc;
size_t i;
int n;

if (virFileReadAll(xmlFile, VSH_MAX_XML_FILE, &buffer) < 0)
goto error;

- if (virAsprintf(&xmlStr, "<container>%s</container>", buffer) < 0)
+ /* Strip possible XML declaration */
+ if (STRPREFIX(buffer, "<?xml") && (doc = strstr(buffer, "?>")))
+ doc += 2;
+ else
+ doc = buffer;
+
+ if (virAsprintf(&xmlStr, "<container>%s</container>", doc) < 0)
goto error;

if (!(xml = virXMLParseStringCtxt(xmlStr, xmlFile, &ctxt)))

[Ján Tomko]

Post by Jiri Denemark
Since commit v4.3.0-336-gc84726fbdd all
{hypervisor-,}cpu-{baseline,compare} commands use a generic
vshExtractCPUDefXMLs helper for extracting individual CPU definitions
from the provided input file. The helper wraps the input file in a
<container> element so that several independent elements can be easily
parsed from the file. This works fine except when the file starts with
XML declaration (<?xml version="1.0" ... ?>) because the XML declaration
cannot be put inside any element. In fact it has to be at the very
beginning of the XML document without any preceding white space
characters. We can just simply skip the XML declaration.

What if someone specifies a doctype? O:)
Also, does libvirt produce such files? I don't think we should bother
doing extra work to undo the extra work done by the user.

Post by Jiri Denemark
https://bugzilla.redhat.com/show_bug.cgi?id=1595993

I only see a relation between the bug summary and this patch.
There's no mention of the XML declaration there and no mention of the
other issues mentioned there here in the patch.

Jano

Post by Jiri Denemark
---
tools/virsh-host.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)

[Jiri Denemark]

Post by Ján Tomko

Post by Jiri Denemark
Since commit v4.3.0-336-gc84726fbdd all
{hypervisor-,}cpu-{baseline,compare} commands use a generic
vshExtractCPUDefXMLs helper for extracting individual CPU definitions
from the provided input file. The helper wraps the input file in a
<container> element so that several independent elements can be easily
parsed from the file. This works fine except when the file starts with
XML declaration (<?xml version="1.0" ... ?>) because the XML declaration
cannot be put inside any element. In fact it has to be at the very
beginning of the XML document without any preceding white space
characters. We can just simply skip the XML declaration.

What if someone specifies a doctype? O:)
Also, does libvirt produce such files? I don't think we should bother
doing extra work to undo the extra work done by the user.

Of course, we don't generate XML declarations, but I can imagine tools
formatting DOM into a file could just automatically output the XML
declaration unless you explicitly tell them not to do so. On the other
hand, nothing would output a doctype or <?xml-stylesheet ?> without an
explicit action.

Moreover, libvirt itself doesn't mind XML declarations and virsh before
4.4.0 didn't mind either.

I agree, it's probably a corner case and I was thinking about not fixing
it, but it turned out to be really easy thanks to the strict XML
specification.

Post by Ján Tomko

Post by Jiri Denemark
https://bugzilla.redhat.com/show_bug.cgi?id=1595993

I only see a relation between the bug summary and this patch.
There's no mention of the XML declaration there and no mention of the
other issues mentioned there here in the patch.

Oops, the patch is supposed to fix another bug
https://bugzilla.redhat.com/show_bug.cgi?id=1592737

Jirka

[Ján Tomko]

Post by Jiri Denemark

Post by Ján Tomko

Post by Jiri Denemark
Since commit v4.3.0-336-gc84726fbdd all
{hypervisor-,}cpu-{baseline,compare} commands use a generic
vshExtractCPUDefXMLs helper for extracting individual CPU definitions
from the provided input file. The helper wraps the input file in a
<container> element so that several independent elements can be easily
parsed from the file. This works fine except when the file starts with
XML declaration (<?xml version="1.0" ... ?>) because the XML declaration
cannot be put inside any element. In fact it has to be at the very
beginning of the XML document without any preceding white space
characters. We can just simply skip the XML declaration.

What if someone specifies a doctype? O:)
Also, does libvirt produce such files? I don't think we should bother
doing extra work to undo the extra work done by the user.

Of course, we don't generate XML declarations, but I can imagine tools
formatting DOM into a file could just automatically output the XML
declaration unless you explicitly tell them not to do so. On the other
hand, nothing would output a doctype or <?xml-stylesheet ?> without an
explicit action.
Moreover, libvirt itself doesn't mind XML declarations and virsh before
4.4.0 didn't mind either.
I agree, it's probably a corner case and I was thinking about not fixing
it, but it turned out to be really easy thanks to the strict XML
specification.

Post by Ján Tomko

Post by Jiri Denemark
https://bugzilla.redhat.com/show_bug.cgi?id=1595993

I only see a relation between the bug summary and this patch.
There's no mention of the XML declaration there and no mention of the
other issues mentioned there here in the patch.

Oops, the patch is supposed to fix another bug
https://bugzilla.redhat.com/show_bug.cgi?id=1592737

With the bug link fixed:

Reviewed-by: Ján Tomko <***@redhat.com>

Jano