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 ?

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); xmlIndentTreeOutput = oldIndentTreeOutput; } diff --git a/src/conf/network_conf.c b/src/conf/network_conf.c index a9eadff29c..20c6dc091a 100644 --- a/src/conf/network_conf.c +++ b/src/conf/network_conf.c @@ -2488,6 +2488,7 @@ virNetworkDefFormatBuf(virBuffer *buf, if (def->metadata) { g_autoptr(xmlBuffer) xmlbuf = NULL; + const char *xmlbufContent = NULL; int oldIndentTreeOutput = xmlIndentTreeOutput; /* Indentation on output requires that we previously set @@ -2504,7 +2505,13 @@ virNetworkDefFormatBuf(virBuffer *buf, 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);

xmlIndentTreeOutput = oldIndentTreeOutput; } -- 2.26.3