[CRIU] [PATCH 2/8] Handling iov generation for non-PROT_READ regions

[Abhishek Dubey]

Skip iov-generation for regions not having
PROT_READ, since process_vm_readv syscall
can't process them during "read" pre-dump.
Handle random order of "read" & "splice"
pre-dumps.

Signed-off-by: Abhishek Dubey <dubeyabhishek777 at gmail.com>
---
 criu/cr-dump.c         |  5 +++++
 criu/mem.c             | 56 ++++++++++++++++++++++++++++++++++++++++++++++++--
 images/inventory.proto |  1 +
 3 files changed, 60 insertions(+), 2 deletions(-)

diff --git a/criu/cr-dump.c b/criu/cr-dump.c
index 119c82d..03f6487 100644
--- a/criu/cr-dump.c
+++ b/criu/cr-dump.c
@@ -1486,6 +1486,9 @@ static int cr_pre_dump_finish(int status)
 	if (ret)
 		goto err;
 
+	he.has_pre_dump_mode = true;
+	he.pre_dump_mode = opts.pre_dump_mode;
+
 	pstree_switch_state(root_item, TASK_ALIVE);
 
 	timing_stop(TIME_FROZEN);
@@ -1930,6 +1933,8 @@ int cr_dump_tasks(pid_t pid)
 	if (ret)
 		goto err;
 
+	he.has_pre_dump_mode = false;
+
 	ret = write_img_inventory(&he);
 	if (ret)
 		goto err;
diff --git a/criu/mem.c b/criu/mem.c
index 911b9d2..a5de237 100644
--- a/criu/mem.c
+++ b/criu/mem.c
@@ -351,7 +351,8 @@ static int generate_vma_iovs(struct pstree_item *item, struct vma_area *vma,
 			     struct page_pipe *pp, struct page_xfer *xfer,
 			     struct parasite_dump_pages_args *args,
 			     struct parasite_ctl *ctl, pmc_t *pmc,
-			     bool has_parent, bool pre_dump)
+			     bool has_parent, bool pre_dump,
+			     int parent_predump_mode)
 {
 	u64 off = 0;
 	u64 *map;
@@ -361,6 +362,52 @@ static int generate_vma_iovs(struct pstree_item *item, struct vma_area *vma,
 				!vma_area_is(vma, VMA_ANON_SHARED))
 		return 0;
 
+	/*
+	 * To facilitate any combination of pre-dump modes to run after
+	 * one another, we need to take extra care as discussed below.
+	 *
+	 * The SPLICE mode pre-dump, processes all type of memory regions,
+	 * whereas READ mode pre-dump skips processing those memory regions
+	 * which lacks PROT_READ flag.
+	 *
+	 * Now on mixing pre-dump modes:
+	 * 	If SPLICE mode follows SPLICE mode	: no issue
+	 *		-> everything dumped both the times
+	 *
+	 * 	If READ mode follows READ mode		: no issue
+	 *		-> non-PROT_READ skipped both the time
+	 *
+	 * 	If READ mode follows SPLICE mode   	: no issue
+	 *		-> everything dumped at first,
+	 *		   the non-PROT_READ skipped later
+	 *
+	 * 	If SPLICE mode follows READ mode   	: Need special care
+	 *
+	 * If READ pre-dump happens first, then it has skipped processing
+	 * non-PROT_READ regions. Following SPLICE pre-dump expects pagemap
+	 * entries for all mappings in parent pagemap, but last READ mode
+	 * pre-dump cycle has skipped processing & pagemap generation for
+	 * non-PROT_READ regions. So SPLICE mode throws error of missing
+	 * pagemap entry for encountered non-PROT_READ mapping.
+	 *
+	 * To resolve this, the pre-dump-mode is stored in current pre-dump's
+	 * inventoy file. This pre-dump mode is read back from this file
+	 * (present in parent pre-dump dir) as parent-pre-dump-mode during
+	 * next pre-dump.
+	 *
+	 * If parent-pre-dump-mode and next-pre-dump-mode are in READ-mode ->
+	 * SPLICE-mode order, then SPLICE mode doesn't expect mappings for
+	 * non-PROT_READ regions in parent-image and marks "has_parent=false".
+	 */
+
+	if (!(vma->e->prot & PROT_READ)) {
+		if (opts.pre_dump_mode == PRE_DUMP_READ && pre_dump)
+			return 0;
+		if ((parent_predump_mode == PRE_DUMP_READ &&
+			opts.pre_dump_mode == PRE_DUMP_SPLICE) || !pre_dump)
+			has_parent = false;
+	}
+
 	if (vma_entry_is(vma->e, VMA_AREA_AIORING)) {
 		if (pre_dump)
 			return 0;
@@ -406,6 +453,7 @@ static int __parasite_dump_pages_seized(struct pstree_item *item,
 	unsigned long pmc_size;
 	int possible_pid_reuse = 0;
 	bool has_parent;
+	int parent_predump_mode = -1;
 
 	pr_info("\n");
 	pr_info("Dumping pages (type: %d pid: %d)\n", CR_FD_PAGES, item->pid->real);
@@ -472,9 +520,13 @@ static int __parasite_dump_pages_seized(struct pstree_item *item,
 	 */
 	args->off = 0;
 	has_parent = !!xfer.parent && !possible_pid_reuse;
+	if(mdc->parent_ie)
+		parent_predump_mode = mdc->parent_ie->pre_dump_mode;
+
 	list_for_each_entry(vma_area, &vma_area_list->h, list) {
 		ret = generate_vma_iovs(item, vma_area, pp, &xfer, args, ctl,
-					&pmc, has_parent, mdc->pre_dump);
+					&pmc, has_parent, mdc->pre_dump,
+					parent_predump_mode);
 		if (ret < 0)
 			goto out_xfer;
 	}
diff --git a/images/inventory.proto b/images/inventory.proto
index 7bc2b0c..d1438e8 100644
--- a/images/inventory.proto
+++ b/images/inventory.proto
@@ -16,4 +16,5 @@ message inventory_entry {
 	optional uint32			root_cg_set	= 5;
 	optional lsmtype		lsmtype		= 6;
 	optional uint64			dump_uptime	= 8;
+	optional uint32			pre_dump_mode	= 9;
 }
-- 
2.7.4