make file updates atomic

While we have locks against other invocations of build-docbook-catalog
to keep them from clobbering each other (write locks), we didn't have
any locks for users of the databases (read locks).  Rewriting the files
in place causes those readers to get partially written files and then
fail (due to missing entries).

Closes: https://bugs.gentoo.org/773517
Signed-off-by: Mike Frysinger <vapier@gentoo.org>

1 files changed, 31 insertions, 20 deletions

diff --git a/build-docbook-catalog b/build-docbook-catalog
index 017ae75..b420541 100755
--- a/build-docbook-catalog
+++ b/build-docbook-catalog
@@ -84,8 +84,8 @@ main() {
 
 	# Clean out old dtds from catalog
 	verb "Cleaning out old DocBook XML versions from ${CATALOG} and ${ROOTCATALOG}"
-	clean_catalog "${DOCBOOKDIR}/xml\(-simple\)*-dtd-[^/\"']*/[^/\"']*" "${CATALOG}"
-	clean_catalog "${DOCBOOKDIR}/xml\(-simple\)*-dtd-[^/\"']*/[^/\"']*" "${ROOTCATALOG}"
+	clean_catalog "${DOCBOOKDIR}/xml\(-simple\)*-dtd-[^/\"']*/[^/\"']*" "${CATALOG}.tmp"
+	clean_catalog "${DOCBOOKDIR}/xml\(-simple\)*-dtd-[^/\"']*/[^/\"']*" "${ROOTCATALOG}.tmp"
 
 	if set_dtds; then
 		for d in "${DTDS[@]}"; do
@@ -97,6 +97,14 @@ main() {
 		populate_entities
 	fi
 
+	sed -i \
+		-e "s:${ROOTCATALOG}\.tmp:${ROOTCATALOG}:g" \
+		-e "s:${CATALOG}\.tmp:${CATALOG}:g" \
+		"${ROOT}${ROOTCATALOG}.tmp" \
+		"${ROOT}${CATALOG}.tmp" || error "could not clean up"
+	mv "${ROOT}${ROOTCATALOG}.tmp" "${ROOT}${ROOTCATALOG}"
+	mv "${ROOT}${CATALOG}.tmp" "${ROOT}${CATALOG}"
+
 	# NB: Don't delete the lock since we can't delete files by fd, and if we do
 	# it by path, we might delete the lock while other processes grab it.
 	) 200>>"${lock}"
@@ -173,11 +181,13 @@ create_catalogs() {
 		if [[ ! -r ${ROOT}${ROOTCATALOG} ]] ; then
 			error "failed creating ${ROOTCATALOG}"
 		fi
+		cp "${ROOT}${ROOTCATALOG}" "${ROOT}${ROOTCATALOG}.tmp"
 	else
 		verb "Found XML Catalog root ${ROOTCATALOG}"
 		# clean out existing entries
 		verb "  Cleaning existing ${CATALOG} delegates from ${ROOTCATALOG}"
-		clean_catalog "file://${CATALOG}" "${ROOTCATALOG}"
+		cp "${ROOTCATALOG}" "${ROOTCATALOG}.tmp"
+		clean_catalog "file://${CATALOG}" "${ROOTCATALOG}.tmp"
 	fi
 
 	# Initialize catalogs if they don't exist or are corrupt.
@@ -194,24 +204,25 @@ create_catalogs() {
 	else
 		verb "Found DocBook XML Catalog ${CATALOG}"
 	fi
+	cp "${ROOT}${CATALOG}" "${ROOT}${CATALOG}.tmp"
 
 	# dtd pointers
 	verb "  Populating ${ROOTCATALOG} with DTD delegates to ${CATALOG}"
 	adds=(
-		"delegatePublic"  "-//OASIS//ENTITIES DocBook"          "${CATALOG}"
-		"delegatePublic"  "-//OASIS//ELEMENTS DocBook"          "${CATALOG}"
-		"delegatePublic"  "-//OASIS//DTD DocBook"               "${CATALOG}"
-		"delegateSystem"  "http://www.oasis-open.org/docbook/"  "${CATALOG}"
-		"delegateURI"     "http://www.oasis-open.org/docbook/"  "${CATALOG}"
+		"delegatePublic"  "-//OASIS//ENTITIES DocBook"          "${CATALOG}.tmp"
+		"delegatePublic"  "-//OASIS//ELEMENTS DocBook"          "${CATALOG}.tmp"
+		"delegatePublic"  "-//OASIS//DTD DocBook"               "${CATALOG}.tmp"
+		"delegateSystem"  "http://www.oasis-open.org/docbook/"  "${CATALOG}.tmp"
+		"delegateURI"     "http://www.oasis-open.org/docbook/"  "${CATALOG}.tmp"
 	)
-	multi_xmlcatalog_add "${ROOTCATALOG}" "${adds[@]}"
+	multi_xmlcatalog_add "${ROOTCATALOG}.tmp" "${adds[@]}"
 
 	# entities pointer
 	verb "  Populating ${ROOTCATALOG} with ISO entities delegate to ${CATALOG}"
 	adds=(
-		"delegatePublic"  "ISO 8879:1986"  "${CATALOG}"
+		"delegatePublic"  "ISO 8879:1986"  "${CATALOG}.tmp"
 	)
-	multi_xmlcatalog_add "${ROOTCATALOG}" "${adds[@]}"
+	multi_xmlcatalog_add "${ROOTCATALOG}.tmp" "${adds[@]}"
 }
 
 #
@@ -259,7 +270,7 @@ populate_dtd() {
 		"rewriteSystem"  "http://www.oasis-open.org/docbook/xml/${v}"                            "${docbookdir}"
 		"rewriteURI"     "http://www.oasis-open.org/docbook/xml/${v}"                            "${docbookdir}"
 	)
-	multi_xmlcatalog_add "${CATALOG}" "${adds[@]}"
+	multi_xmlcatalog_add "${CATALOG}.tmp" "${adds[@]}"
 
 	# grab the RCS date from docbookx.dtd for comparison purposes
 	if [[ ! -f ${ROOT}${docbookdir}/ent/iso-lat1.ent ]]; then
@@ -305,7 +316,7 @@ populate_simple_dtd() {
 		"rewriteSystem"  "http://www.oasis-open.org/docbook/xml/simple/${v}"  "${docbookdir}"
 		"rewriteURI"     "http://www.oasis-open.org/docbook/xml/simple/${v}"  "${docbookdir}"
 	)
-	multi_xmlcatalog_add "${CATALOG}" "${adds[@]}"
+	multi_xmlcatalog_add "${CATALOG}.tmp" "${adds[@]}"
 }
 
 #
@@ -367,7 +378,7 @@ populate_entities() {
 			: $(( i += 2 ))
 		elif [[ ${entities[i]} == "${avail[j]}" ]]; then
 			xmlcatalog --noout --add "public" "${entities[i+1]}" \
-				"file://${isodir}/${entities[i]}" "${ROOT}${CATALOG}"
+				"file://${isodir}/${entities[i]}" "${ROOT}${CATALOG}.tmp"
 			: $(( j += 1 ))
 			: $(( i += 2 ))
 		else
@@ -386,8 +397,8 @@ populate_xsl() {
 	local type=$1
 
 	# Delete current entries from the catalog (delete legacy versioned entries too)
-	clean_catalog "${DOCBOOKDIR}/${type}-stylesheets(-[0-9\.]+)?" "${CATALOG}"
-	clean_catalog "${DOCBOOKDIR}/${type}-stylesheets(-[0-9\.]+)?" "${ROOTCATALOG}"
+	clean_catalog "${DOCBOOKDIR}/${type}-stylesheets(-[0-9\.]+)?" "${CATALOG}.tmp"
+	clean_catalog "${DOCBOOKDIR}/${type}-stylesheets(-[0-9\.]+)?" "${ROOTCATALOG}.tmp"
 
 	local xsldir=${DOCBOOKDIR}/${type}-stylesheets
 
@@ -406,17 +417,17 @@ populate_xsl() {
 
 	verb "  Populating ${ROOTCATALOG} with XSL delegations"
 	adds=(
-		"delegateSystem"  "http://docbook.sourceforge.net/release/${type}/"  "${CATALOG}"
-		"delegateURI"     "http://docbook.sourceforge.net/release/${type}/"  "${CATALOG}"
+		"delegateSystem"  "http://docbook.sourceforge.net/release/${type}/"  "${CATALOG}.tmp"
+		"delegateURI"     "http://docbook.sourceforge.net/release/${type}/"  "${CATALOG}.tmp"
 	)
-	multi_xmlcatalog_add "${ROOTCATALOG}" "${adds[@]}"
+	multi_xmlcatalog_add "${ROOTCATALOG}.tmp" "${adds[@]}"
 
 	verb "  Populating ${CATALOG} with XSL stylesheets"
 	adds=(
 		"rewriteSystem"  "http://docbook.sourceforge.net/release/${type}/current"  "${xsldir}"
 		"rewriteURI"     "http://docbook.sourceforge.net/release/${type}/current"  "${xsldir}"
 	)
-	multi_xmlcatalog_add "${CATALOG}" "${adds[@]}"
+	multi_xmlcatalog_add "${CATALOG}.tmp" "${adds[@]}"
 }
 
 # Call the main routine