tools lib fd array: Allow associating an integer cookie with each entry

We will use this in perf's evlist class so that it can, at
fdarray__filter() time, to unmap the associated ring buffer.

We may need to have further info associated with each fdarray entry, in
that case we'll make that int array a 'union fdarray_priv' one and put a
pointer there so that users can stash whatever they want there. For now,
an int is enough tho.

v2: Add clarification to the per array entry priv area, as well as make
    it a union, which makes usage a bit longer, but if/when we make it
    use more space by allowing per entry pointers existing users source
    code will not have to be changed, just rebuilt.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Borislav Petkov <bp@suse.de>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jean Pihet <jean.pihet@linaro.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

Link: http://lkml.kernel.org/n/tip-0p00bn83quck3fio3kcs9vca@git.kernel.org

2 files changed, 39 insertions, 5 deletions

diff --git a/tools/lib/api/fd/array.c b/tools/lib/api/fd/array.c
index 4889c7d42961..0e636c4339b8 100644
--- a/tools/lib/api/fd/array.c
+++ b/tools/lib/api/fd/array.c
@@ -13,21 +13,31 @@
 void fdarray__init(struct fdarray *fda, int nr_autogrow)
 {
         fda->entries     = NULL;
+        fda->priv        = NULL;
         fda->nr          = fda->nr_alloc = 0;
         fda->nr_autogrow = nr_autogrow;
 }
 
 int fdarray__grow(struct fdarray *fda, int nr)
 {
+        void *priv;
         int nr_alloc = fda->nr_alloc + nr;
+        size_t psize = sizeof(fda->priv[0]) * nr_alloc;
         size_t size  = sizeof(struct pollfd) * nr_alloc;
         struct pollfd *entries = realloc(fda->entries, size);
 
         if (entries == NULL)
                 return -ENOMEM;
 
+        priv = realloc(fda->priv, psize);
+        if (priv == NULL) {
+                free(entries);
+                return -ENOMEM;
+        }
+
         fda->nr_alloc = nr_alloc;
         fda->entries  = entries;
+        fda->priv     = priv;
         return 0;
 }
 
@@ -50,6 +60,7 @@ struct fdarray *fdarray__new(int nr_alloc, int nr_autogrow)
 void fdarray__exit(struct fdarray *fda)
 {
         free(fda->entries);
+        free(fda->priv);
         fdarray__init(fda, 0);
 }
 
@@ -61,6 +72,8 @@ void fdarray__delete(struct fdarray *fda)
 
 int fdarray__add(struct fdarray *fda, int fd, short revents)
 {
+        int pos = fda->nr;
+
         if (fda->nr == fda->nr_alloc &&
             fdarray__grow(fda, fda->nr_autogrow) < 0)
                 return -ENOMEM;
@@ -68,10 +81,11 @@ int fdarray__add(struct fdarray *fda, int fd, short revents)
         fda->entries[fda->nr].fd     = fd;
         fda->entries[fda->nr].events = revents;
         fda->nr++;
-        return 0;
+        return pos;
 }
 
-int fdarray__filter(struct fdarray *fda, short revents)
+int fdarray__filter(struct fdarray *fda, short revents,
+                    void (*entry_destructor)(struct fdarray *fda, int fd))
 {
         int fd, nr = 0;
 
@@ -79,11 +93,17 @@ int fdarray__filter(struct fdarray *fda, short revents)
                 return 0;
 
         for (fd = 0; fd < fda->nr; ++fd) {
-                if (fda->entries[fd].revents & revents)
+                if (fda->entries[fd].revents & revents) {
+                        if (entry_destructor)
+                                entry_destructor(fda, fd);
+
                         continue;
+                }
 
-                if (fd != nr)
+                if (fd != nr) {
                         fda->entries[nr] = fda->entries[fd];
+                        fda->priv[nr]    = fda->priv[fd];
+                }
 
                 ++nr;
         }
diff --git a/tools/lib/api/fd/array.h b/tools/lib/api/fd/array.h
index de38361ba69e..45db01818f45 100644
--- a/tools/lib/api/fd/array.h
+++ b/tools/lib/api/fd/array.h
@@ -5,11 +5,24 @@
 
 struct pollfd;
 
+/**
+ * struct fdarray: Array of file descriptors
+ *
+ * @priv: Per array entry priv area, users should access just its contents,
+ *        not set it to anything, as it is kept in synch with @entries, being
+ *        realloc'ed, * for instance, in fdarray__{grow,filter}.
+ *
+ *        I.e. using 'fda->priv[N].idx = * value' where N < fda->nr is ok,
+ *        but doing 'fda->priv = malloc(M)' is not allowed.
+ */
 struct fdarray {
         int            nr;
         int            nr_alloc;
         int            nr_autogrow;
         struct pollfd *entries;
+        union {
+                int    idx;
+        } *priv;
 };
 
 void fdarray__init(struct fdarray *fda, int nr_autogrow);
@@ -20,7 +33,8 @@ void fdarray__delete(struct fdarray *fda);
 
 int fdarray__add(struct fdarray *fda, int fd, short revents);
 int fdarray__poll(struct fdarray *fda, int timeout);
-int fdarray__filter(struct fdarray *fda, short revents);
+int fdarray__filter(struct fdarray *fda, short revents,
+                    void (*entry_destructor)(struct fdarray *fda, int fd));
 int fdarray__grow(struct fdarray *fda, int extra);
 int fdarray__fprintf(struct fdarray *fda, FILE *fp);