PR29472: debuginfod: add metadata query webapi, C api, clientusers/fche/try-pr29472e

This patch extends the debuginfod API with a "metadata query"
operation.  It allows clients to request an enumeration of file names
known to debuginfod servers, returning a JSON response including the
matching buildids.  This lets clients later download debuginfo for a
range of versions of the same named binaries, in case they need to to
prospective work (like systemtap-based live-patching).  It also lets
server operators implement prefetch triggering operations for popular
but slow debuginfo slivers like kernel vdso.debug files on fedora.

Implementation requires a modern enough json-c library.

% debuginfod-find metadata file /bin/ls
% debuginfod-find metadata glob "/usr/local/bin/c*"

Documentation and testing are included.

Signed-off-by: Ryan Goldberg <rgoldber@redhat.com>
Signed-off-by: Frank Ch. Eigler <fche@redhat.com>

1 files changed, 15 insertions, 3 deletions

diff --git a/debuginfod/debuginfod.h.in b/debuginfod/debuginfod.h.in
index 4a256ba9..3efa877a 100644
--- a/debuginfod/debuginfod.h.in
+++ b/debuginfod/debuginfod.h.in
@@ -62,9 +62,9 @@ debuginfod_client *debuginfod_begin (void);
    it is a binary blob of given length.
 
    If successful, return a file descriptor to the target, otherwise
-   return a posix error code.  If successful, set *path to a
-   strdup'd copy of the name of the same file in the cache.
-   Caller must free() it later. */
+   return a negative POSIX error code.  If successful, set *path to a
+   strdup'd copy of the name of the same file in the cache.  Caller
+   must free() it later. */
 
 int debuginfod_find_debuginfo (debuginfod_client *client,
 			       const unsigned char *build_id,
@@ -88,6 +88,18 @@ int debuginfod_find_section (debuginfod_client *client,
 			     const char *section,
 			     char **path);
 
+/* Query the urls contained in $DEBUGINFOD_URLS for metadata
+   with given query key/value.
+   
+   If successful, return a file descriptor to the JSON document
+   describing matches, otherwise return a negative POSIX error code.  If
+   successful, set *path to a strdup'd copy of the name of the same
+   file in the cache.  Caller must free() it later. */
+int debuginfod_find_metadata (debuginfod_client *client,
+                              const char *key,
+                              const char* value,
+                              char **path);
+
 typedef int (*debuginfod_progressfn_t)(debuginfod_client *c, long a, long b);
 void debuginfod_set_progressfn(debuginfod_client *c,
 			       debuginfod_progressfn_t fn);