libctf, next: introduce new class of easier-to-use iterators

The libctf machinery currently only provides one way to iterate over its
data structures: ctf_*_iter functions that take a callback and an arg
and repeatedly call it.

This *works*, but if you are doing a lot of iteration it is really quite
inconvenient: you have to package up your local variables into
structures over and over again and spawn lots of little functions even
if it would be clearer in a single run of code.  Look at ctf-string.c
for an extreme example of how unreadable this can get, with
three-line-long functions proliferating wildly.

The deduplicator takes this to the Nth level. It iterates over a whole
bunch of things: if we'd had to use _iter-class iterators for all of
them there would be twenty additional functions in the deduplicator
alone, for no other reason than that the iterator API requires it.

Let's do something better. strtok_r gives us half the design: generators
in a number of other languages give us the other half.

The *_next API allows you to iterate over CTF-like entities in a single
function using a normal while loop. e.g. here we are iterating over all
the types in a dict:

ctf_next_t *i = NULL;
int *hidden;
ctf_id_t id;

while ((id = ctf_type_next (fp, &i, &hidden, 1)) != CTF_ERR)
  {
    /* do something with 'hidden' and 'id' */
  }
if (ctf_errno (fp) != ECTF_NEXT_END)
    /* iteration error */

Here we are walking through the members of a struct with CTF ID
'struct_type':

ctf_next_t *i = NULL;
ssize_t offset;
const char *name;
ctf_id_t membtype;

while ((offset = ctf_member_next (fp, struct_type, &i, &name,
                                  &membtype)) >= 0
  {
    /* do something with offset, name, and membtype */
  }
if (ctf_errno (fp) != ECTF_NEXT_END)
    /* iteration error */

Like every other while loop, this means you have access to all the local
variables outside the loop while inside it, with no need to tiresomely
package things up in structures, move the body of the loop into a
separate function, etc, as you would with an iterator taking a callback.

ctf_*_next allocates 'i' for you on first entry (when it must be NULL),
and frees and NULLs it and returns a _next-dependent flag value when the
iteration is over: the fp errno is set to ECTF_NEXT_END when the
iteartion ends normally.  If you want to exit early, call
ctf_next_destroy on the iterator.  You can copy iterators using
ctf_next_copy, which copies their current iteration position so you can
remember loop positions and go back to them later (or ctf_next_destroy
them if you don't need them after all).

Each _next function returns an always-likely-to-be-useful property of
the thing being iterated over, and takes pointers to parameters for the
others: with very few exceptions all those parameters can be NULLs if
you're not interested in them, so e.g. you can iterate over only the
offsets of members of a structure this way:

while ((offset = ctf_member_next (fp, struct_id, &i, NULL, NULL)) >= 0)

If you pass an iterator in use by one iteration function to another one,
you get the new error ECTF_NEXT_WRONGFUN back; if you try to change
ctf_file_t in mid-iteration, you get ECTF_NEXT_WRONGFP back.

Internally the ctf_next_t remembers the iteration function in use,
various sizes and increments useful for almost all iterations, then
uses unions to overlap the actual entities being iterated over to keep
ctf_next_t size down.

Iterators available in the public API so far (all tested in actual use
in the deduplicator):

/* Iterate over the members of a STRUCT or UNION, returning each member's
   offset and optionally name and member type in turn.  On end-of-iteration,
   returns -1.  */
ssize_t
ctf_member_next (ctf_file_t *fp, ctf_id_t type, ctf_next_t **it,
                 const char **name, ctf_id_t *membtype);

/* Iterate over the members of an enum TYPE, returning each enumerand's
   NAME or NULL at end of iteration or error, and optionally passing
   back the enumerand's integer VALue.  */
const char *
ctf_enum_next (ctf_file_t *fp, ctf_id_t type, ctf_next_t **it,
              int *val);

/* Iterate over every type in the given CTF container (not including
   parents), optionally including non-user-visible types, returning
   each type ID and optionally the hidden flag in turn. Returns CTF_ERR
   on end of iteration or error.  */
ctf_id_t
ctf_type_next (ctf_file_t *fp, ctf_next_t **it, int *flag,
               int want_hidden);

/* Iterate over every variable in the given CTF container, in arbitrary
   order, returning the name and type of each variable in turn.  The
   NAME argument is not optional.  Returns CTF_ERR on end of iteration
   or error.  */
ctf_id_t
ctf_variable_next (ctf_file_t *fp, ctf_next_t **it, const char **name);

/* Iterate over all CTF files in an archive, returning each dict in turn as a
   ctf_file_t, and NULL on error or end of iteration.  It is the caller's
   responsibility to close it.  Parent dicts may be skipped.  Regardless of
   whether they are skipped or not, the caller must ctf_import the parent if
   need be.  */
ctf_file_t *
ctf_archive_next (const ctf_archive_t *wrapper, ctf_next_t **it,
                  const char **name, int skip_parent, int *errp);

ctf_label_next is prototyped but not implemented yet.

include/
	* ctf-api.h (ECTF_NEXT_END): New error.
	(ECTF_NEXT_WRONGFUN): Likewise.
	(ECTF_NEXT_WRONGFP): Likewise.
	(ECTF_NERR): Adjust.
	(ctf_next_t): New.
	(ctf_next_create): New prototype.
	(ctf_next_destroy): Likewise.
	(ctf_next_copy): Likewise.
	(ctf_member_next): Likewise.
	(ctf_enum_next): Likewise.
	(ctf_type_next): Likewise.
	(ctf_label_next): Likewise.
	(ctf_variable_next): Likewise.

libctf/
	* ctf-impl.h (ctf_next): New.
	(ctf_get_dict): New prototype.
	* ctf-lookup.c (ctf_get_dict): New, split out of...
	(ctf_lookup_by_id): ... here.
	* ctf-util.c (ctf_next_create): New.
	(ctf_next_destroy): New.
	(ctf_next_copy): New.
	* ctf-types.c (includes): Add <assert.h>.
	(ctf_member_next): New.
	(ctf_enum_next): New.
	(ctf_type_iter): Document the lack of iteration over parent
	types.
	(ctf_type_next): New.
	(ctf_variable_next): New.
	* ctf-archive.c (ctf_archive_next): New.
	* libctf.ver: Add new public functions.

libctf/ctf-types.c

@@ -18,6 +18,7 @@
    <http://www.gnu.org/licenses/>.  */
 
 #include <ctf-impl.h>
+#include <assert.h>
 #include <string.h>
 
 /* Determine whether a type is a parent or a child.  */
@@ -103,6 +104,125 @@ ctf_member_iter (ctf_file_t *fp, ctf_id_t type, ctf_member_f *func, void *arg)
   return 0;
 }
 
+/* Iterate over the members of a STRUCT or UNION, returning each member's
+   offset and optionally name and member type in turn.  On end-of-iteration,
+   returns -1.  */
+
+ssize_t
+ctf_member_next (ctf_file_t *fp, ctf_id_t type, ctf_next_t **it,
+		 const char **name, ctf_id_t *membtype)
+{
+  ctf_file_t *ofp = fp;
+  uint32_t kind;
+  ssize_t offset;
+  ctf_next_t *i = *it;
+
+  if (!i)
+    {
+      const ctf_type_t *tp;
+      ctf_dtdef_t *dtd;
+
+      if ((type = ctf_type_resolve (fp, type)) == CTF_ERR)
+	return -1;			/* errno is set for us.  */
+
+      if ((tp = ctf_lookup_by_id (&fp, type)) == NULL)
+	return -1;			/* errno is set for us.  */
+
+      if ((i = ctf_next_create ()) == NULL)
+	return ctf_set_errno (ofp, ENOMEM);
+      i->cu.ctn_fp = ofp;
+
+      (void) ctf_get_ctt_size (fp, tp, &i->ctn_size,
+			       &i->ctn_increment);
+      kind = LCTF_INFO_KIND (fp, tp->ctt_info);
+
+      if (kind != CTF_K_STRUCT && kind != CTF_K_UNION)
+	{
+	  ctf_next_destroy (i);
+	  return (ctf_set_errno (ofp, ECTF_NOTSOU));
+	}
+
+      dtd = ctf_dynamic_type (fp, type);
+      i->ctn_iter_fun = (void (*) (void)) ctf_member_next;
+
+      /* We depend below on the RDWR state indicating whether the DTD-related
+	 fields or the DMD-related fields have been initialized.  */
+
+      assert ((dtd && (fp->ctf_flags & LCTF_RDWR))
+	      || (!dtd && (!(fp->ctf_flags & LCTF_RDWR))));
+
+      if (dtd == NULL)
+	{
+	  i->ctn_n = LCTF_INFO_VLEN (fp, tp->ctt_info);
+
+	  if (i->ctn_size < CTF_LSTRUCT_THRESH)
+	    i->u.ctn_mp = (const ctf_member_t *) ((uintptr_t) tp +
+						  i->ctn_increment);
+	  else
+	    i->u.ctn_lmp = (const ctf_lmember_t *) ((uintptr_t) tp +
+						    i->ctn_increment);
+	}
+      else
+	i->u.ctn_dmd = ctf_list_next (&dtd->dtd_u.dtu_members);
+
+      *it = i;
+    }
+
+  if ((void (*) (void)) ctf_member_next != i->ctn_iter_fun)
+    return (ctf_set_errno (ofp, ECTF_NEXT_WRONGFUN));
+
+  if (ofp != i->cu.ctn_fp)
+    return (ctf_set_errno (ofp, ECTF_NEXT_WRONGFP));
+
+  /* Resolve to the native dict of this type.  */
+  if ((fp = ctf_get_dict (ofp, type)) == NULL)
+    return (ctf_set_errno (ofp, ECTF_NOPARENT));
+
+  if (!(fp->ctf_flags & LCTF_RDWR))
+    {
+      if (i->ctn_n == 0)
+	goto end_iter;
+
+      if (i->ctn_size < CTF_LSTRUCT_THRESH)
+	{
+	  if (name)
+	    *name = ctf_strptr (fp, i->u.ctn_mp->ctm_name);
+	  if (membtype)
+	    *membtype = i->u.ctn_mp->ctm_type;
+	  offset = i->u.ctn_mp->ctm_offset;
+	  i->u.ctn_mp++;
+	}
+      else
+	{
+	  if (name)
+	    *name = ctf_strptr (fp, i->u.ctn_lmp->ctlm_name);
+	  if (membtype)
+	    *membtype = i->u.ctn_lmp->ctlm_type;
+	  offset = (unsigned long) CTF_LMEM_OFFSET (i->u.ctn_lmp);
+	  i->u.ctn_lmp++;
+	}
+      i->ctn_n--;
+    }
+  else
+    {
+      if (i->u.ctn_dmd == NULL)
+	goto end_iter;
+      if (name)
+	*name = i->u.ctn_dmd->dmd_name;
+      if (membtype)
+	*membtype = i->u.ctn_dmd->dmd_type;
+      offset = i->u.ctn_dmd->dmd_offset;
+      i->u.ctn_dmd = ctf_list_next (i->u.ctn_dmd);
+    }
+
+  return offset;
+
+ end_iter:
+  ctf_next_destroy (i);
+  *it = NULL;
+  return ctf_set_errno (ofp, ECTF_NEXT_END);
+}
+
 /* Iterate over the members of an ENUM.  We pass the string name and associated
    integer value of each enum element to the specified callback function.  */
 
@@ -154,8 +274,126 @@ ctf_enum_iter (ctf_file_t *fp, ctf_id_t type, ctf_enum_f *func, void *arg)
   return 0;
 }
 
+/* Iterate over the members of an enum TYPE, returning each enumerand's NAME or
+   NULL at end of iteration or error, and optionally passing back the
+   enumerand's integer VALue.  */
+
+const char *
+ctf_enum_next (ctf_file_t *fp, ctf_id_t type, ctf_next_t **it,
+	       int *val)
+{
+  ctf_file_t *ofp = fp;
+  uint32_t kind;
+  const char *name;
+  ctf_next_t *i = *it;
+
+  if (!i)
+    {
+      const ctf_type_t *tp;
+      ctf_dtdef_t *dtd;
+
+      if ((type = ctf_type_resolve_unsliced (fp, type)) == CTF_ERR)
+	return NULL;			/* errno is set for us.  */
+
+      if ((tp = ctf_lookup_by_id (&fp, type)) == NULL)
+	return NULL;			/* errno is set for us.  */
+
+      if ((i = ctf_next_create ()) == NULL)
+	{
+	  ctf_set_errno (ofp, ENOMEM);
+	  return NULL;
+	}
+      i->cu.ctn_fp = ofp;
+
+      (void) ctf_get_ctt_size (fp, tp, NULL,
+			       &i->ctn_increment);
+      kind = LCTF_INFO_KIND (fp, tp->ctt_info);
+
+      if (kind != CTF_K_ENUM)
+	{
+	  ctf_next_destroy (i);
+	  ctf_set_errno (ofp, ECTF_NOTENUM);
+	  return NULL;
+	}
+
+      dtd = ctf_dynamic_type (fp, type);
+      i->ctn_iter_fun = (void (*) (void)) ctf_enum_next;
+
+      /* We depend below on the RDWR state indicating whether the DTD-related
+	 fields or the DMD-related fields have been initialized.  */
+
+      assert ((dtd && (fp->ctf_flags & LCTF_RDWR))
+	      || (!dtd && (!(fp->ctf_flags & LCTF_RDWR))));
+
+      if (dtd == NULL)
+	{
+	  i->ctn_n = LCTF_INFO_VLEN (fp, tp->ctt_info);
+
+	  i->u.ctn_en = (const ctf_enum_t *) ((uintptr_t) tp +
+					      i->ctn_increment);
+	}
+      else
+	i->u.ctn_dmd = ctf_list_next (&dtd->dtd_u.dtu_members);
+
+      *it = i;
+    }
+
+  if ((void (*) (void)) ctf_enum_next != i->ctn_iter_fun)
+    {
+      ctf_set_errno (ofp, ECTF_NEXT_WRONGFUN);
+      return NULL;
+    }
+
+  if (ofp != i->cu.ctn_fp)
+    {
+      ctf_set_errno (ofp, ECTF_NEXT_WRONGFP);
+      return NULL;
+    }
+
+  /* Resolve to the native dict of this type.  */
+  if ((fp = ctf_get_dict (ofp, type)) == NULL)
+    {
+      ctf_set_errno (ofp, ECTF_NOPARENT);
+      return NULL;
+    }
+
+  if (!(fp->ctf_flags & LCTF_RDWR))
+    {
+      if (i->ctn_n == 0)
+	goto end_iter;
+
+      name = ctf_strptr (fp, i->u.ctn_en->cte_name);
+      if (val)
+	*val = i->u.ctn_en->cte_value;
+      i->u.ctn_en++;
+      i->ctn_n--;
+    }
+  else
+    {
+      if (i->u.ctn_dmd == NULL)
+	goto end_iter;
+
+      name = i->u.ctn_dmd->dmd_name;
+      if (val)
+	*val = i->u.ctn_dmd->dmd_value;
+      i->u.ctn_dmd = ctf_list_next (i->u.ctn_dmd);
+    }
+
+  return name;
+
+ end_iter:
+  ctf_next_destroy (i);
+  *it = NULL;
+  ctf_set_errno (ofp, ECTF_NEXT_END);
+  return NULL;
+}
+
 /* Iterate over every root (user-visible) type in the given CTF container.
-   We pass the type ID of each type to the specified callback function.  */
+   We pass the type ID of each type to the specified callback function.
+
+   Does not traverse parent types: you have to do that explicitly.  This is by
+   design, to avoid traversing them more than once if traversing many children
+   of a single parent.  */
 
 int
 ctf_type_iter (ctf_file_t *fp, ctf_type_f *func, void *arg)
@@ -175,7 +413,11 @@ ctf_type_iter (ctf_file_t *fp, ctf_type_f *func, void *arg)
 }
 
 /* Iterate over every type in the given CTF container, user-visible or not.
-   We pass the type ID of each type to the specified callback function.  */
+   We pass the type ID of each type to the specified callback function.
+
+   Does not traverse parent types: you have to do that explicitly.  This is by
+   design, to avoid traversing them more than once if traversing many children
+   of a single parent.  */
 
 int
 ctf_type_iter_all (ctf_file_t *fp, ctf_type_all_f *func, void *arg)
@@ -195,6 +437,55 @@ ctf_type_iter_all (ctf_file_t *fp, ctf_type_all_f *func, void *arg)
   return 0;
 }
 
+/* Iterate over every type in the given CTF container, optionally including
+   non-user-visible types, returning each type ID and hidden flag in turn.
+   Returns CTF_ERR on end of iteration or error.
+
+   Does not traverse parent types: you have to do that explicitly.  This is by
+   design, to avoid traversing them more than once if traversing many children
+   of a single parent.  */
+
+ctf_id_t
+ctf_type_next (ctf_file_t *fp, ctf_next_t **it, int *flag, int want_hidden)
+{
+  ctf_next_t *i = *it;
+
+  if (!i)
+    {
+      if ((i = ctf_next_create ()) == NULL)
+	return ctf_set_errno (fp, ENOMEM);
+
+      i->cu.ctn_fp = fp;
+      i->ctn_type = 1;
+      i->ctn_iter_fun = (void (*) (void)) ctf_type_next;
+      *it = i;
+    }
+
+  if ((void (*) (void)) ctf_type_next != i->ctn_iter_fun)
+    return (ctf_set_errno (fp, ECTF_NEXT_WRONGFUN));
+
+  if (fp != i->cu.ctn_fp)
+    return (ctf_set_errno (fp, ECTF_NEXT_WRONGFP));
+
+  while (i->ctn_type <= fp->ctf_typemax)
+    {
+      const ctf_type_t *tp = LCTF_INDEX_TO_TYPEPTR (fp, i->ctn_type);
+
+      if ((!want_hidden) && (!LCTF_INFO_ISROOT (fp, tp->ctt_info)))
+	{
+	  i->ctn_type++;
+	  continue;
+	}
+
+      if (flag)
+	*flag = LCTF_INFO_ISROOT (fp, tp->ctt_info);
+      return LCTF_INDEX_TO_TYPE (fp, i->ctn_type++, fp->ctf_flags & LCTF_CHILD);
+    }
+  ctf_next_destroy (i);
+  *it = NULL;
+  return ctf_set_errno (fp, ECTF_NEXT_END);
+}
+
 /* Iterate over every variable in the given CTF container, in arbitrary order.
    We pass the name of each variable to the specified callback function.  */
 
@@ -229,6 +520,63 @@ ctf_variable_iter (ctf_file_t *fp, ctf_variable_f *func, void *arg)
   return 0;
 }
 
+/* Iterate over every variable in the given CTF container, in arbitrary order,
+   returning the name and type of each variable in turn.  The name argument is
+   not optional.  Returns CTF_ERR on end of iteration or error.  */
+
+ctf_id_t
+ctf_variable_next (ctf_file_t *fp, ctf_next_t **it, const char **name)
+{
+  ctf_next_t *i = *it;
+
+  if ((fp->ctf_flags & LCTF_CHILD) && (fp->ctf_parent == NULL))
+    return (ctf_set_errno (fp, ECTF_NOPARENT));
+
+  if (!i)
+    {
+      if ((i = ctf_next_create ()) == NULL)
+	return ctf_set_errno (fp, ENOMEM);
+
+      i->cu.ctn_fp = fp;
+      i->ctn_iter_fun = (void (*) (void)) ctf_variable_next;
+      if (fp->ctf_flags & LCTF_RDWR)
+	i->u.ctn_dvd = ctf_list_next (&fp->ctf_dvdefs);
+      *it = i;
+    }
+
+  if ((void (*) (void)) ctf_variable_next != i->ctn_iter_fun)
+    return (ctf_set_errno (fp, ECTF_NEXT_WRONGFUN));
+
+  if (fp != i->cu.ctn_fp)
+    return (ctf_set_errno (fp, ECTF_NEXT_WRONGFP));
+
+  if (!(fp->ctf_flags & LCTF_RDWR))
+    {
+      if (i->ctn_n >= fp->ctf_nvars)
+	goto end_iter;
+
+      *name = ctf_strptr (fp, fp->ctf_vars[i->ctn_n].ctv_name);
+      return fp->ctf_vars[i->ctn_n++].ctv_type;
+    }
+  else
+    {
+      ctf_id_t id;
+
+      if (i->u.ctn_dvd == NULL)
+	goto end_iter;
+
+      *name = i->u.ctn_dvd->dvd_name;
+      id = i->u.ctn_dvd->dvd_type;
+      i->u.ctn_dvd = ctf_list_next (i->u.ctn_dvd);
+      return id;
+    }
+
+ end_iter:
+  ctf_next_destroy (i);
+  *it = NULL;
+  return ctf_set_errno (fp, ECTF_NEXT_END);
+}
+
 /* Follow a given type through the graph for TYPEDEF, VOLATILE, CONST, and
    RESTRICT nodes until we reach a "base" type node.  This is useful when
    we want to follow a type ID to a node that has members or a size.  To guard