Re: [PATCH for 7.4.0] conf: Avoid double indentation of <metadata/> element

On Tue, May 25, 2021 at 09:32:35AM +0200, Michal Privoznik wrote: > There was a recent change in libxml2 that caused a trouble for > us. To us, <metadata/> in domain or network XMLs are just opaque > value where management application can store whatever data it > finds fit. At XML parser/formatter level, we just make a copy of > the element during parsing and then format it back. For > formatting we use xmlNodeDump() which allows caller to specify > level of indentation. Previously, the indentation was not > applied onto the very first line, but as of v2.9.12-2-g85b1792e > libxml2 is applying indentation also on the first line. > > This does not work well with out virBuffer because as soon as we > call virBufferAsprintf() to append <metadata/> element, > virBufferAsprintf() will apply another level of indentation. > > Instead of version checking, let's skip any indentation added by > libxml2 before virBufferAsprintf() is called. > > Note, the problem is only when telling xmlNodeDump() to use > indentation, i.e. level argument is not zero. Therefore, > virXMLNodeToString() which also calls xmlNodeDump() is safe as it > passes zero. > > Signed-off-by: Michal Privoznik <mprivozn(a)redhat.com&gt; > --- > > I've raised this issue with libxml2 team: > > https://gitlab.gnome.org/GNOME/libxml2/-/commit/85b1792e37b131e7a51af98a3... > > but I'm not sure it'll be fixed. Unfortunately, the patch that's causing > us trouble is being backported all over the place, because it's > supposedly fixing a regression. > > src/conf/domain_conf.c | 9 ++++++++- > src/conf/network_conf.c | 9 ++++++++- > 2 files changed, 16 insertions(+), 2 deletions(-) > > diff --git a/src/conf/domain_conf.c b/src/conf/domain_conf.c > index 4f78b7b43d..84a8c269be 100644 > --- a/src/conf/domain_conf.c > +++ b/src/conf/domain_conf.c > @@ -27808,6 +27808,7 @@ virDomainDefFormatInternalSetRootName(virDomainDef *def, > > if (def->metadata) { > g_autoptr(xmlBuffer) xmlbuf = NULL; > + const char *xmlbufContent = NULL; > int oldIndentTreeOutput = xmlIndentTreeOutput; > > /* Indentation on output requires that we previously set > @@ -27824,7 +27825,13 @@ virDomainDefFormatInternalSetRootName(virDomainDef *def, > xmlIndentTreeOutput = oldIndentTreeOutput; > return -1; > } > - virBufferAsprintf(buf, "%s\n", (char *) xmlBufferContent(xmlbuf)); > + > + /* After libxml2-v2.9.12-2-g85b1792e even the first line is indented. > + * But virBufferAsprintf() also adds indentation. Skip one of them. */ > + xmlbufContent = (const char *) xmlBufferContent(xmlbuf); > + virSkipSpaces(&xmlbufContent); > + > + virBufferAsprintf(buf, "%s\n", xmlbufContent); Won't this mean that indent is now wrong for the older libxml ?