[DTrace-devel] [PATCH 4/5] Implement dt_bpf_map_lookup_inner() and dt_bpf_map_update_inner()

[Eugene Loh]

Reviewed-by: Eugene Loh <eugene.loh at oracle.com>

For the dt_bpf_map_get_fd_by_id() comment, I assume:
s/based on it id/based on its id/

Personally, instead of key1/key2, it'd be better to stick to the in/out terminology that is otherwise used.  In fact, converting "name[key1][key2]" to the in/out terminology would be a nice way of illustrating what in/out mean.

Will dt_bpf_map_get_fd_by_id() be used outside this file?  That is, should it be "static" rather than declared in dt_bpf.h?

________________________________
From: Kris Van Hees via DTrace-devel <dtrace-devel at oss.oracle.com>
Sent: Friday, August 19, 2022 10:26 AM
To: dtrace-devel at oss.oracle.com <dtrace-devel at oss.oracle.com>
Subject: [DTrace-devel] [PATCH 4/5] Implement dt_bpf_map_lookup_inner() and dt_bpf_map_update_inner()

Signed-off-by: Kris Van Hees <kris.van.hees at oracle.com>
---
 libdtrace/dt_bpf.c | 59 ++++++++++++++++++++++++++++++++++++++++++++++
 libdtrace/dt_bpf.h |  5 ++++
 2 files changed, 64 insertions(+)

diff --git a/libdtrace/dt_bpf.c b/libdtrace/dt_bpf.c
index 7a886278..66c76022 100644
--- a/libdtrace/dt_bpf.c
+++ b/libdtrace/dt_bpf.c
@@ -164,6 +164,20 @@ dt_bpf_map_create_meta(enum bpf_map_type otype, const char *name,
         return ofd;
 }

+/*
+ * Get a file descriptor for a BPF map based on it id.
+ */
+int
+dt_bpf_map_get_fd_by_id(uint32_t id)
+{
+       union bpf_attr  attr;
+
+       memset(&attr, 0, sizeof(attr));
+       attr.map_id = id;
+
+       return bpf(BPF_MAP_GET_FD_BY_ID, &attr);
+}
+
 /*
  * Load the value for the given key in the map referenced by the given fd.
  */
@@ -228,6 +242,51 @@ dt_bpf_map_update(int fd, const void *key, const void *val)
         return bpf(BPF_MAP_UPDATE_ELEM, &attr);
 }

+/*
+ * Retrieve the value in a map-of-maps, i.e. map[key1][key2] = value.
+ */
+int
+dt_bpf_map_lookup_inner(int fd, const void *key1, const void *key2, void *val)
+{
+       uint32_t        id;
+       int             rc;
+
+       if (dt_bpf_map_lookup(fd, key1, &id) < 0)
+               return -1;
+
+       fd = dt_bpf_map_get_fd_by_id(id);
+       if (fd < 0)
+               return -1;
+
+       rc = dt_bpf_map_lookup(fd, key2, val);
+       close(fd);
+
+       return rc;
+}
+
+/*
+ * Store the value in a map-of-maps, i.e. map[key1][key2] = value.
+ */
+int
+dt_bpf_map_update_inner(int fd, const void *key1, const void *key2,
+                       const void *val)
+{
+       uint32_t        id;
+       int             rc;
+
+       if (dt_bpf_map_lookup(fd, key1, &id) < 0)
+               return -1;
+
+       fd = dt_bpf_map_get_fd_by_id(id);
+       if (fd < 0)
+               return -1;
+
+       rc = dt_bpf_map_update(fd, key2, val);
+       close(fd);
+
+       return rc;
+}
+
 static int
 have_helper(uint32_t func_id)
 {
diff --git a/libdtrace/dt_bpf.h b/libdtrace/dt_bpf.h
index f8c75012..7a16c03d 100644
--- a/libdtrace/dt_bpf.h
+++ b/libdtrace/dt_bpf.h
@@ -50,6 +50,11 @@ extern int dt_bpf_map_lookup(int fd, const void *key, void *val);
 extern int dt_bpf_map_next_key(int fd, const void *key, void *nxt);
 extern int dt_bpf_map_update(int fd, const void *key, const void *val);
 extern int dt_bpf_map_delete(int fd, const void *key);
+extern int dt_bpf_map_get_fd_by_id(uint32_t id);
+extern int dt_bpf_map_lookup_inner(int fd, const void *key1, const void *key2,
+                                  void *val);
+extern int dt_bpf_map_update_inner(int fd, const void *key1, const void *key2,
+                                  const void *val);
 extern int dt_bpf_load_progs(struct dtrace_hdl *, uint_t);
 extern void dt_bpf_init_helpers(struct dtrace_hdl *dtp);

--
2.34.1


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