di-set: manipulate sets of dev/inode pairs efficiently

* gl/lib/di-set.c: Implementation.
* gl/lib/di-set.h: Declarations.
* gl/modules/di-set: Define module.
* gl/modules/di-set-tests: Define test module.
* gl/tests/test-di-set.c: Likewise.

1 files changed, 276 insertions, 0 deletions

diff --git a/gl/lib/di-set.c b/gl/lib/di-set.c
new file mode 100644
index 000000000..3c4717b73
--- /dev/null
+++ b/gl/lib/di-set.c
@@ -0,0 +1,276 @@
+/* Set operations for device-inode pairs stored in a space-efficient manner.
+
+   Copyright 2009-2010 Free Software Foundation, Inc.
+
+   This program is free software: you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+/* written by Jim Meyering */
+
+#include <config.h>
+#include "di-set.h"
+
+#include <stdio.h>
+#include <assert.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+
+#include "verify.h"
+
+/* Set operations for device-inode pairs stored in a space-efficient manner.
+   A naive mapping uses 16 bytes to save a single st_dev, st_ino pair.
+   However, in many applications, the vast majority of actual device,inode
+   number pairs can be efficiently compressed to fit in 8 or even 4 bytes,
+   by using a separate table to map a relatively small number of devices
+   to small integers.  */
+
+#define N_DEV_BITS_4 5
+#define N_INO_BITS_4 (32 - N_DEV_BITS_4 - 2 - 1)
+
+#define N_DEV_BITS_8 8
+#define N_INO_BITS_8 (64 - N_DEV_BITS_8 - 2 - 1)
+
+/* Note how the last bit is always set.
+   This is required, in order to be able to distinguish
+   an encoded di_ent value from a malloc-returned pointer,
+   which must be 4-byte-aligned or better.  */
+struct dev_ino_4
+{
+  uint32_t mode:2; /* must be first */
+  uint32_t short_ino:N_INO_BITS_4;
+  uint32_t mapped_dev:N_DEV_BITS_4;
+  uint32_t always_set:1;
+};
+verify (N_DEV_BITS_4 <= 8 * sizeof (int));
+verify (sizeof (struct dev_ino_4) == 4);
+
+struct dev_ino_8
+{
+  uint32_t mode:2; /* must be first */
+  uint64_t short_ino:N_INO_BITS_8;
+  uint32_t mapped_dev:N_DEV_BITS_8;
+  uint32_t always_set:1;
+};
+verify (sizeof (struct dev_ino_8) == 8);
+
+struct dev_ino_full
+{
+  uint32_t mode:2; /* must be first */
+  dev_t dev;
+  ino_t ino;
+};
+
+enum di_mode
+{
+  DI_MODE_4 = 1,
+  DI_MODE_8 = 2,
+  DI_MODE_FULL = 3
+};
+
+/*
+     di_mode     raw_inode      mapped dev    always_set
+          \____________|_______________\_____/
+  4-byte | 2|          25            |  5  |1|          mapped_dev
+         `----------------------------------------------------|-----.
+  8-byte | 2|        53                                  |    8   |1|
+         `----------------------------------------------------------'
+*/
+struct di_ent
+{
+  union
+  {
+    struct dev_ino_4 di4;
+    struct dev_ino_8 di8;
+    struct dev_ino_full full;
+    uint32_t u32;
+    uint64_t u64;
+    void *ptr;
+  } u;
+};
+
+struct dev_map_ent
+{
+  dev_t dev;
+  uint32_t mapped_dev;
+};
+
+static inline bool
+is_encoded_ptr (struct di_ent const *v)
+{
+  return (size_t) v % 4;
+}
+
+static struct di_ent
+decode_ptr (struct di_ent const *v)
+{
+  if (!is_encoded_ptr (v))
+    return *v;
+
+  struct di_ent di;
+  di.u.ptr = (void *) v;
+  return di;
+}
+
+static size_t
+di_ent_hash (void const *x, size_t table_size)
+{
+  struct di_ent e = decode_ptr (x);
+  return (e.u.di4.mode == DI_MODE_4
+          ? e.u.u32
+          : (e.u.di4.mode == DI_MODE_8
+             ? e.u.u64
+             : e.u.full.ino)) % table_size;
+}
+
+/* Compare two di_ent structs.
+   Return true if they are the same.  */
+static bool
+di_ent_compare (void const *x, void const *y)
+{
+  struct di_ent a = decode_ptr (x);
+  struct di_ent b = decode_ptr (y);
+  if (a.u.di4.mode != b.u.di4.mode)
+    return false;
+
+  if (a.u.di4.mode == DI_MODE_4)
+    return (a.u.di4.short_ino == b.u.di4.short_ino
+            && a.u.di4.mapped_dev == b.u.di4.mapped_dev);
+
+  if (a.u.di8.mode == DI_MODE_8)
+    return (a.u.di8.short_ino == b.u.di8.short_ino
+            && a.u.di8.mapped_dev == b.u.di8.mapped_dev);
+
+  return (a.u.full.ino == b.u.full.ino
+          && a.u.full.dev == b.u.full.dev);
+}
+
+static void
+di_ent_free (void *v)
+{
+  if ( ! is_encoded_ptr (v))
+    free (v);
+}
+
+int
+di_set_init (struct di_set_state *dis, size_t initial_size)
+{
+  if (dev_map_init (&dis->dev_map) < 0)
+    return -1;
+
+  dis->di_set = hash_initialize (initial_size, NULL,
+                                 di_ent_hash, di_ent_compare, di_ent_free);
+  return dis->di_set ? 0 : -1;
+}
+
+void
+di_set_free (struct di_set_state *dis)
+{
+  dev_map_free (&dis->dev_map);
+  hash_free (dis->di_set);
+}
+
+/* Given a device-inode set, DIS, create an entry for the DEV,INO
+   pair, and store it in *V.  If possible, encode DEV,INO into the pointer
+   itself, but if not, allocate space for a full "struct di_ent" and set *V
+   to that pointer.  Upon memory allocation failure, return -1.
+   Otherwise return 0.  */
+int
+di_ent_create (struct di_set_state *dis,
+               dev_t dev, ino_t ino,
+               struct di_ent **v)
+{
+  static int prev_m = -1;
+  static dev_t prev_dev = -1;
+  struct di_ent di_ent;
+  int mapped_dev;
+
+  if (dev == prev_dev)
+    mapped_dev = prev_m;
+  else
+    {
+      mapped_dev = dev_map_insert (&dis->dev_map, dev);
+      if (mapped_dev < 0)
+        return -1;
+      prev_dev = dev;
+      prev_m = mapped_dev;
+    }
+
+  if (mapped_dev < (1 << N_DEV_BITS_4)
+      && ino < (1 << N_INO_BITS_4))
+    {
+#if lint
+      /* When this struct is smaller than a pointer, initialize
+         the pointer so tools like valgrind don't complain about
+         the uninitialized bytes.  */
+      if (sizeof di_ent.u.di4 < sizeof di_ent.u.ptr)
+        di_ent.u.ptr = NULL;
+#endif
+      di_ent.u.di4.mode = DI_MODE_4;
+      di_ent.u.di4.short_ino = ino;
+      di_ent.u.di4.mapped_dev = mapped_dev;
+      di_ent.u.di4.always_set = 1;
+      *v = di_ent.u.ptr;
+    }
+  else if (mapped_dev < (1 << N_DEV_BITS_8)
+           && ino < ((uint64_t) 1 << N_INO_BITS_8))
+    {
+      di_ent.u.di8.mode = DI_MODE_8;
+      di_ent.u.di8.short_ino = ino;
+      di_ent.u.di8.mapped_dev = mapped_dev;
+      di_ent.u.di8.always_set = 1;
+      *v = di_ent.u.ptr;
+    }
+  else
+    {
+      /* Handle the case in which INO is too large or in which (far less
+         likely) we encounter hard-linked files on 2^N_DEV_BITS_8
+         different devices.  */
+      struct di_ent *p = malloc (sizeof *p);
+      if (!p)
+        return -1;
+      assert ((size_t) p % 4 == 0);
+      p->u.full.mode = DI_MODE_FULL;
+      p->u.full.ino = ino;
+      p->u.full.dev = dev;
+      *v = p;
+    }
+
+  return 0;
+}
+
+/* Attempt to insert the DEV,INO pair into the set, DIS.
+   If it matches a pair already in DIS, don't modify DIS and return 0.
+   Otherwise, if insertion is successful, return 1.
+   Upon any failure return -1.  */
+int
+di_set_insert (struct di_set_state *dis, dev_t dev, ino_t ino)
+{
+  struct di_ent *v;
+  if (di_ent_create (dis, dev, ino, &v) < 0)
+    return -1;
+
+  int err = hash_insert0 (dis->di_set, v, NULL);
+  if (err == -1) /* Insertion failed due to lack of memory.  */
+    return -1;
+
+  if (err == 1) /* Insertion succeeded.  */
+    return 1;
+
+  /* That pair is already in the table, so ENT was not inserted.  Free it.  */
+  if (! is_encoded_ptr (v))
+    free (v);
+
+  return 0;
+}