get-linux-source: fixup for prepare-incremental-build

.github/workflows/kernel-build.yml

@@ -46,11 +46,6 @@ jobs:
     timeout-minutes: 100
     env:
         ARTIFACTS_ARCHIVE: "vmlinux-${{ inputs.arch }}-${{ inputs.toolchain_full }}.tar.zst"
-        BASE_BRANCH: >-
-          ${{ github.event_name == 'push' && github.ref_name
-              || github.base_ref
-              || 'bpf-next'
-          }}
         BUILD_SCHED_EXT_SELFTESTS: ${{ inputs.arch == 'x86_64' || inputs.arch == 'aarch64' && 'true' || '' }}
         CACHED_KERNEL_BUILD: ${{ github.event_name == 'push' || github.repository == 'libbpf/ci'  && 'true' || '' }}
         KBUILD_OUTPUT: ${{ github.workspace }}/kbuild-output
@@ -67,33 +62,31 @@ jobs:
       - if: ${{ inputs.download_sources }}
         name: Download bpf-next tree
         env:
-          FETCH_GIT_REPO: ${{ env.CACHED_KERNEL_BUILD }}
+          FETCH_DEPTH: ${{ env.CACHED_KERNEL_BUILD && 16 || 0 }}
         uses: ./get-linux-source
         with:
           dest: '.kernel'
-      - if: ${{ inputs.download_sources }}
-        name: Move linux source in place
-        shell: bash
-        run: |
-          mv .git /tmp/.git.not-kernel
-          cd .kernel
-          mv -t .. $(ls -A)
-          cd ..
-          rmdir .kernel
       - if: ${{ env.CACHED_KERNEL_BUILD }}
         uses: ./prepare-incremental-build
         with:
-          repo-root: ${{ env.REPO_ROOT }}
-          base-branch: ${{ env.BASE_BRANCH }}
+          repo-root: ${{ inputs.download_sources && '.kernel' || env.REPO_ROOT }}
+          base-branch: >-
+            ${{    github.repository == 'kernel-patches/bpf' && github.event_name == 'push' && github.ref_name
+                || github.repository == 'kernel-patches/bpf' && github.event_name != 'push' && github.base_ref
+                || 'master'
+             }}
           arch: ${{ inputs.arch }}
           toolchain_full: ${{ inputs.toolchain_full }}
           kbuild-output: ${{ env.KBUILD_OUTPUT }}
       - if: ${{ inputs.download_sources }}
-        name: Restore .git # is this really necessary?
+        name: Move linux source in place
         shell: bash
         run: |
+          cd .kernel
           rm -rf .git
-          mv /tmp/.git.not-kernel .git
+          mv -t .. $(ls -A)
+          cd ..
+          rmdir .kernel
       - uses:  ./patch-kernel
         with:
           patches-root: '${{ github.workspace }}/ci/diffs'

get-linux-source/checkout_latest_kernel.sh

@@ -6,7 +6,8 @@ source $(cd $(dirname $0) && pwd)/../helpers.sh
 
 CWD=$(pwd)
 
-FETCH_GIT_REPO=${FETCH_GIT_REPO:-}
+# 0 means just download a snapshot
+FETCH_DEPTH=${FETCH_DEPTH:-0}
 
 echo KERNEL_ORIGIN = ${KERNEL_ORIGIN}
 echo KERNEL_BRANCH = ${KERNEL_BRANCH}
@@ -31,28 +32,27 @@ if [ ! -d "${REPO_PATH}" ]; then
 	mkdir -p $(dirname "${REPO_PATH}")
 	cd $(dirname "${REPO_PATH}")
 	# attempt to fetch desired bpf-next repo snapshot
-	if [ -n "${SNAPSHOT_URL}" ] && [ -z "${FETCH_GIT_REPO}" ] && \
+	if [ -n "${SNAPSHOT_URL}" ] && [ "${FETCH_DEPTH}" -eq 0 ] && \
 	   wget -U 'BPFCIBot/1.0 ([email protected])' -nv ${SNAPSHOT_URL} && \
 	   tar xf bpf-next-${LINUX_SHA}.tar.gz --totals ; then
 		mv bpf-next-${LINUX_SHA} $(basename ${REPO_PATH})
 	else
-		# but fallback to git fetch approach if that fails
-		mkdir -p $(basename ${REPO_PATH})
-		cd $(basename ${REPO_PATH})
-		git init
-		git remote add bpf-next ${KERNEL_ORIGIN}
-		# try shallow clone first
-		git fetch --depth 32 bpf-next
-		# check if desired SHA exists
-		if ! git cat-file -e ${LINUX_SHA}^{commit} ; then
-			# if not, fetch all of bpf-next; slow and painful
-			git fetch bpf-next
-		fi
-		git reset --hard ${LINUX_SHA}
+	    # but fallback to git fetch approach if that fails
+            git clone --depth ${FETCH_DEPTH} ${KERNEL_ORIGIN} ${REPO_PATH}
+            cd "${REPO_PATH}"
+	    # check if desired SHA exists
+	    if ! git cat-file -e ${LINUX_SHA}^{commit} ; then
+                # if not, fetch all of bpf-next; slow and painful
+                git fetch origin
+            fi
+            git reset --hard ${LINUX_SHA}
+            cd -
 	fi
-        if [ -z "${FETCH_GIT_REPO}" ]; then
+        if [ "${FETCH_DEPTH}" -eq 0 ]; then
 	    rm -rf ${REPO_PATH}/.git || true
         fi
 
 	foldable end pull_kernel_srcs
+else
+    echo "${REPO_PATH} directory already exists, will not download kernel sources"
 fi