libdpkg: Switch to a new tiny struct to track file ondisk identity

We only need the device and inode numbers for a given file to be able to
compare them for identity. Avoid storing the entire struct stat which is
rather fat.

4 files changed, 25 insertions, 11 deletions

diff --git a/debian/changelog b/debian/changelog
index 4fa07bb48..a3ab57e77 100644
--- a/debian/changelog
+++ b/debian/changelog
@@ -187,6 +187,8 @@ dpkg (1.19.1) UNRELEASED; urgency=medium
     - libdpkg: Simplify pkg_files_blank() by using a pointer to pointer to
       track the previous entry.
     - libdpkg: Factor out package files handling into its own module.
+    - libdpkg: Switch to a new tiny struct to track file on-disk identity.
+      This should reduce the run-time memory used.
   * Build system:
     - Set distribution tarball format to ustar, instead of default v7 format.
     - Mark PO4A and POD2MAN as precious variables.
diff --git a/lib/dpkg/fsys-hash.c b/lib/dpkg/fsys-hash.c
index 54d0d57b7..15d9669b4 100644
--- a/lib/dpkg/fsys-hash.c
+++ b/lib/dpkg/fsys-hash.c
@@ -51,7 +51,7 @@ filesdbinit(void)
 			fnn->flags = 0;
 			fnn->oldhash = NULL;
 			fnn->newhash = EMPTYHASHFLAG;
-			fnn->filestat = NULL;
+			fnn->file_ondisk_id = NULL;
 		}
 	}
 }
@@ -117,7 +117,7 @@ findnamenode(const char *name, enum fnnflags flags)
 	newnode->statoverride = NULL;
 	newnode->oldhash = NULL;
 	newnode->newhash = EMPTYHASHFLAG;
-	newnode->filestat = NULL;
+	newnode->file_ondisk_id = NULL;
 	newnode->trig_interested = NULL;
 	*pointerp = newnode;
 	nfiles++;
diff --git a/lib/dpkg/fsys.h b/lib/dpkg/fsys.h
index 7d63b04e6..8a2efbffa 100644
--- a/lib/dpkg/fsys.h
+++ b/lib/dpkg/fsys.h
@@ -77,6 +77,14 @@ enum filenamenode_flags {
 	fnnf_filtered			= DPKG_BIT(9),
 };
 
+/**
+ * Stores information to uniquely identify an on-disk file.
+ */
+struct file_ondisk_id {
+	dev_t id_dev;
+	ino_t id_ino;
+};
+
 struct filenamenode {
 	struct filenamenode *next;
 	const char *name;
@@ -105,7 +113,7 @@ struct filenamenode {
 	/** Valid iff the file was unpacked and hashed on this run. */
 	const char *newhash;
 
-	struct stat *filestat;
+	struct file_ondisk_id *file_ondisk_id;
 };
 
 /**
diff --git a/src/unpack.c b/src/unpack.c
index 827211d63..cae756222 100644
--- a/src/unpack.c
+++ b/src/unpack.c
@@ -608,7 +608,7 @@ pkg_remove_old_files(struct pkginfo *pkg,
     } else {
       struct fileinlist *sameas = NULL;
       struct fileinlist *cfile;
-      static struct stat empty_stat;
+      static struct file_ondisk_id empty_ondisk_id;
       struct varbuf cfilename = VARBUF_INIT;
 
       /*
@@ -637,7 +637,7 @@ pkg_remove_old_files(struct pkginfo *pkg,
         if (cfile->namenode->flags & fnnf_filtered)
           continue;
 
-        if (!cfile->namenode->filestat) {
+        if (cfile->namenode->file_ondisk_id == NULL) {
           struct stat tmp_stat;
 
           varbuf_reset(&cfilename);
@@ -646,22 +646,26 @@ pkg_remove_old_files(struct pkginfo *pkg,
           varbuf_end_str(&cfilename);
 
           if (lstat(cfilename.buf, &tmp_stat) == 0) {
-            cfile->namenode->filestat = nfmalloc(sizeof(struct stat));
-            memcpy(cfile->namenode->filestat, &tmp_stat, sizeof(struct stat));
+            struct file_ondisk_id *file_ondisk_id;
+
+            file_ondisk_id = nfmalloc(sizeof(*file_ondisk_id));
+            file_ondisk_id->id_dev = tmp_stat.st_dev;
+            file_ondisk_id->id_ino = tmp_stat.st_ino;
+            cfile->namenode->file_ondisk_id = file_ondisk_id;
           } else {
             if (!(errno == ENOENT || errno == ELOOP || errno == ENOTDIR))
               ohshite(_("unable to stat other new file '%.250s'"),
                       cfile->namenode->name);
-            cfile->namenode->filestat = &empty_stat;
+            cfile->namenode->file_ondisk_id = &empty_ondisk_id;
             continue;
           }
         }
 
-        if (cfile->namenode->filestat == &empty_stat)
+        if (cfile->namenode->file_ondisk_id == &empty_ondisk_id)
           continue;
 
-        if (oldfs.st_dev == cfile->namenode->filestat->st_dev &&
-            oldfs.st_ino == cfile->namenode->filestat->st_ino) {
+        if (oldfs.st_dev == cfile->namenode->file_ondisk_id->id_dev &&
+            oldfs.st_ino == cfile->namenode->file_ondisk_id->id_ino) {
           if (sameas)
             warning(_("old file '%.250s' is the same as several new files! "
                       "(both '%.250s' and '%.250s')"), fnamevb.buf,