[CRIU] [PATCH 5/7] irmap: Revalidate irmap entries if required

[Pavel Emelyanov]

We will load some irmap entries in cache from image file,
thus producing potentially stale data in irmap cache. To
handle this, make it possible to mark the entries with
need-revalidation mark and do fstat + numbers comparison
when meeting the entry in cache.

Signed-off-by: Pavel Emelyanov <xemul at parallels.com>
---
 irmap.c | 56 +++++++++++++++++++++++++++++++++++++++++++++++---------
 1 file changed, 47 insertions(+), 9 deletions(-)

diff --git a/irmap.c b/irmap.c
index aca773d..7d326c4 100644
--- a/irmap.c
+++ b/irmap.c
@@ -39,7 +39,7 @@ struct irmap {
 	unsigned long ino;
 	char *path;
 	struct irmap *next;
-
+	bool revalidate;
 	int nr_kids;
 	struct irmap *kids;
 };
@@ -69,6 +69,7 @@ static int irmap_update_stat(struct irmap *i)
 		return -1;
 	}
 
+	i->revalidate = false;
 	i->dev = st.st_dev;
 	i->ino = st.st_ino;
 	if (!S_ISDIR(st.st_mode))
@@ -172,28 +173,65 @@ static struct irmap *irmap_scan(struct irmap *t, unsigned int dev, unsigned long
 	return NULL;
 }
 
+static int irmap_revalidate(struct irmap *c, struct irmap **p)
+{
+	struct stat st;
+
+	pr_debug("Revalidate stat for %s\n", c->path);
+	if (fstatat(mntns_root, c->path + 1, &st, AT_SYMLINK_NOFOLLOW)) {
+		/* File can be (re)moved, so just treat it as invalid */
+		pr_perror("Can't stat %s", c->path);
+		goto invalid;
+	}
+
+	if (c->dev != st.st_dev)
+		goto invalid;
+	if (c->ino != st.st_ino)
+		goto invalid;
+
+	c->revalidate = false;
+	return 0;
+
+invalid:
+	pr_debug("\t%x:%lx is invalid\n", c->dev, c->ino);
+	*p = c->next;
+	xfree(c->path);
+	xfree(c);
+	return 1;
+}
+
 char *irmap_lookup(unsigned int s_dev, unsigned long i_ino)
 {
-	struct irmap *c, *h;
+	struct irmap *c, *h, **p;
+	char *path = NULL;
 	int hv;
 
 	pr_debug("Resolving %x:%lx path\n", s_dev, i_ino);
 
 	hv = irmap_hashfn(s_dev, i_ino);
-	for (c = cache[hv]; c; c = c->next)
-		if (c->dev == s_dev && c->ino == i_ino) {
-			pr_debug("\tFound %s in cache\n", c->path);
-			return c->path;
-		}
+	for (p = &cache[hv]; *p; p = &(*p)->next) {
+		c = *p;
+		if (!(c->dev == s_dev && c->ino == i_ino))
+			continue;
+
+		if (c->revalidate && irmap_revalidate(c, p))
+			continue;
+
+		pr_debug("\tFound %s in cache\n", c->path);
+		path = c->path;
+		goto out;
+	}
 
 	for (h = hints; h->path; h++) {
 		pr_debug("Scanning %s hint\n", h->path);
 		c = irmap_scan(h, s_dev, i_ino);
 		if (c) {
 			pr_debug("\tScanned %s\n", c->path);
-			return c->path;
+			path = c->path;
+			goto out;
 		}
 	}
 
-	return NULL;
+out:
+	return path;
 }
-- 
1.8.4.2