[CRIU] [PATCH] lazy-pages: add comments to update_lazy_iovecs

[Mike Rapoport]

This function does weird things, so better have it at least somehow
documented.

Signed-off-by: Mike Rapoport <rppt at linux.vnet.ibm.com>
---
 criu/uffd.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/criu/uffd.c b/criu/uffd.c
index d71a83a..716bada 100644
--- a/criu/uffd.c
+++ b/criu/uffd.c
@@ -325,6 +325,10 @@ static MmEntry *init_mm_entry(struct lazy_pages_info *lpi)
 	return mm;
 }
 
+/*
+ * Purge range (addr, addr + len) from lazy_iovecs. The range may
+ * cover several continuous IOVs.
+ */
 static int update_lazy_iovecs(struct lazy_pages_info *lpi, unsigned long addr,
 			      int len)
 {
@@ -340,6 +344,13 @@ static int update_lazy_iovecs(struct lazy_pages_info *lpi, unsigned long addr,
 		if (addr < start || addr >= end)
 			continue;
 
+		/*
+		 * The range completely fits into the current IOV.
+		 * If addr equals iov_base we just "drop" the
+		 * beginning of the IOV. Otherwise, we make the IOV to
+		 * end at addr, and add a new IOV start starts at
+		 * addr + len.
+		 */
 		if (addr + len < end) {
 			if (addr == start) {
 				lazy_iov->base += len;
@@ -361,6 +372,12 @@ static int update_lazy_iovecs(struct lazy_pages_info *lpi, unsigned long addr,
 			break;
 		}
 
+		/*
+		 * The range spawns beyond the end of the current IOV.
+		 * If addr equals iov_base we just "drop" the entire
+		 * IOV.  Otherwise, we cut the beginning of the IOV
+		 * and continue to the next one with the updated range
+		 */
 		if (addr == start) {
 			list_del(&lazy_iov->l);
 			xfree(lazy_iov);
-- 
1.9.1