libctf: mmappable archives

If you need to store a large number of CTF containers somewhere, this
provides a dedicated facility for doing so: an mmappable archive format
like a very simple tar or ar without all the system-dependent format
horrors or need for heavy file copying, with built-in compression of
files above a particular size threshold.

libctf automatically mmap()s uncompressed elements of these archives, or
uncompresses them, as needed.  (If the platform does not support mmap(),
copying into dynamically-allocated buffers is used.)

Archive iteration operations are partitioned into raw and non-raw
forms. Raw operations pass thhe raw archive contents to the callback:
non-raw forms open each member with ctf_bufopen() and pass the resulting
ctf_file_t to the iterator instead.  This lets you manipulate the raw
data in the archive, or the contents interpreted as a CTF file, as
needed.

It is not yet known whether we will store CTF archives in a linked ELF
object in one of these (akin to debugdata) or whether they'll get one
section per TU plus one parent container for types shared between them.
(In the case of ELF objects with very large numbers of TUs, an archive
of all of them would seem preferable, so we might just use an archive,
and add lzma support so you can assume that .gnu_debugdata and .ctf are
compressed using the same algorithm if both are present.)

To make usage easier, the ctf_archive_t is not the on-disk
representation but an abstraction over both ctf_file_t's and archives of
many ctf_file_t's: users see both CTF archives and raw CTF files as
ctf_archive_t's upon opening, the only difference being that a raw CTF
file has only a single "archive member", named ".ctf" (the default if a
null pointer is passed in as the name).  The next commit will make use
of this facility, in addition to providing the public interface to
actually open archives.  (In the future, it should be possible to have
all CTF sections in an ELF file appear as an "archive" in the same
fashion.)

This machinery is also used to allow library-internal creators of
ctf_archive_t's (such as the next commit) to stash away an ELF string
and symbol table, so that all opens of members in a given archive will
use them.  This lets CTF archives exploit the ELF string and symbol
table just like raw CTF files can.

(All this leads to somewhat confusing type naming.  The ctf_archive_t is
a typedef for the opaque internal type, struct ctf_archive_internal: the
non-internal "struct ctf_archive" is the on-disk structure meant for
other libraries manipulating CTF files.  It is probably clearest to use
the struct name for struct ctf_archive_internal inside the program, and
the typedef names outside.)

libctf/
	* ctf-archive.c: New.
	* ctf-impl.h (ctf_archive_internal): New type.
	(ctf_arc_open_internal): New declaration.
	(ctf_arc_bufopen): Likewise.
	(ctf_arc_close_internal): Likewise.
include/
	* ctf.h (CTFA_MAGIC): New.
	(struct ctf_archive): New.
	(struct ctf_archive_modent): Likewise.
	* ctf-api.h (ctf_archive_member_f): New.
	(ctf_archive_raw_member_f): Likewise.
	(ctf_arc_write): Likewise.
	(ctf_arc_close): Likewise.
	(ctf_arc_open_by_name): Likewise.
	(ctf_archive_iter): Likewise.
	(ctf_archive_raw_iter): Likewise.
	(ctf_get_arc): Likewise.

1 files changed, 30 insertions, 0 deletions

diff --git a/include/ctf-api.h b/include/ctf-api.h
index d9eff0bc284..4cac635e57e 100644
--- a/include/ctf-api.h
+++ b/include/ctf-api.h
@@ -198,13 +198,35 @@ enum
 #define	CTF_ADD_NONROOT	0	/* Type only visible in nested scope.  */
 #define	CTF_ADD_ROOT	1	/* Type visible at top-level scope.  */
 
+/* These typedefs are used to define the signature for callback functions
+   that can be used with the iteration and visit functions below.  */
+
+typedef int ctf_archive_member_f (ctf_file_t *fp, const char *name, void *arg);
+typedef int ctf_archive_raw_member_f (const char *name, const void *content,
+				      size_t len, void *arg);
+
 extern ctf_sect_t ctf_getdatasect (const ctf_file_t *);
+extern ctf_archive_t *ctf_get_arc (const ctf_file_t *);
+extern void ctf_arc_close (ctf_archive_t *);
+extern ctf_file_t *ctf_arc_open_by_name (const ctf_archive_t *,
+					 const char *, int *);
+extern ctf_file_t *ctf_arc_open_by_name_sections (const ctf_archive_t *,
+						  const ctf_sect_t *,
+						  const ctf_sect_t *,
+						  const char *, int *);
+
+/* The next functions return or close real CTF files, or write out CTF archives,
+   not opaque containers around either.  */
+
 extern ctf_file_t *ctf_simple_open (const char *, size_t, const char *, size_t,
 				   size_t, const char *, size_t, int *);
 extern ctf_file_t *ctf_bufopen (const ctf_sect_t *, const ctf_sect_t *,
 				const ctf_sect_t *, int *);
 extern void ctf_file_close (ctf_file_t *);
 
+extern int ctf_arc_write (const char *, ctf_file_t **, size_t,
+			  const char **, size_t);
+
 extern ctf_file_t *ctf_parent_file (ctf_file_t *);
 extern const char *ctf_parent_name (ctf_file_t *);
 extern void ctf_parent_name_set (ctf_file_t *, const char *);
@@ -218,6 +240,14 @@ extern void *ctf_getspecific (ctf_file_t *);
 
 extern int ctf_errno (ctf_file_t *);
 extern const char *ctf_errmsg (int);
+extern int ctf_archive_iter (const ctf_archive_t *, ctf_archive_member_f *,
+			     void *);
+/* This function alone does not currently operate on CTF files masquerading
+   as archives, and returns -EINVAL: the raw data is no longer available.  It is
+   expected to be used only by archiving tools, in any case, which have no need
+   to deal with non-archives at all.  */
+extern int ctf_archive_raw_iter (const ctf_archive_t *,
+				 ctf_archive_raw_member_f *, void *);
 extern ctf_id_t ctf_add_array (ctf_file_t *, uint32_t,
 			       const ctf_arinfo_t *);
 extern ctf_id_t ctf_add_const (ctf_file_t *, uint32_t, ctf_id_t);