files: Cache special file IDs

We have tons of files with equal IDs, e.g. libraries mapped
to different tasks. No need in writing all this duplicate
stuff into images -- cache the IDs with dev:ino keys.
Acked-by: Andrew Vagin <avagin@parallels.com>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

file-ids.c

@@ -6,7 +6,7 @@
 #include <unistd.h>
 #include <errno.h>
 #include <string.h>
-
+#include <sys/stat.h>
 #include <sys/types.h>
 
 #include "asm/types.h"
@@ -26,9 +26,68 @@ void fd_id_show_tree(void)
 	kid_show_tree(&fd_tree);
 }
 
+#define FDID_BITS	5
+#define FDID_SIZE	(1 << FDID_BITS)
+#define FDID_MASK	(FDID_SIZE - 1)
+
+static inline int fdid_hashfn(unsigned int s_dev, unsigned long i_ino)
+{
+	return (s_dev + i_ino) & FDID_MASK;
+}
+
+struct fd_id {
+	unsigned int dev;
+	unsigned long ino;
+	u32 id;
+	struct fd_id *n;
+};
+
+static struct fd_id *fd_id_cache[FDID_SIZE];
+
+static void fd_id_cache_one(u32 id, struct stat *st)
+{
+	struct fd_id *fi;
+	unsigned hv;
+
+	fi = xmalloc(sizeof(*fi));
+	if (fi) {
+		fi->dev = st->st_dev;
+		fi->ino = st->st_ino;
+		fi->id = id;
+
+		hv = fdid_hashfn(st->st_dev, st->st_ino);
+		fi->n = fd_id_cache[hv];
+		fd_id_cache[hv] = fi;
+	}
+}
+
+static struct fd_id *fd_id_cache_lookup(struct stat *st)
+{
+	struct fd_id *fi;
+
+	for (fi = fd_id_cache[fdid_hashfn(st->st_dev, st->st_ino)];
+			fi; fi = fi->n)
+		if (fi->dev == st->st_dev && fi->ino == st->st_ino)
+			return fi;
+
+	return NULL;
+}
+
 int fd_id_generate_special(struct stat *st, u32 *id)
 {
+	if (st) {
+		struct fd_id *fi;
+
+		fi = fd_id_cache_lookup(st);
+		if (fi) {
+			*id = fi->id;
+			return 0;
+		}
+	}
+
 	*id = fd_tree.subid++;
+	if (st)
+		fd_id_cache_one(*id, st);
 	return 1;
 }
 
@@ -46,6 +105,9 @@ int fd_id_generate(pid_t pid, FdinfoEntry *fe, struct stat *st)
 	if (!id)
 		return -ENOMEM;
 
+	if (new_id)
+		fd_id_cache_one(id, st);
+
 	fe->id = id;
 	return new_id;
 }