Lower the start up memory allocation overhead.

In the vast majority of cases, code will not need to
override the "/proc" root directory, so treat NULL
as equivalent to "/proc".

Signed-off-by: Andrew G. Morgan <agm@google.com>
Signed-off-by: Andrew G. Morgan <morgan@kernel.org>

4 files changed, 16 insertions, 7 deletions

diff --git a/libcap/cap_alloc.c b/libcap/cap_alloc.c
index 4dabe27..f77dec3 100644
--- a/libcap/cap_alloc.c
+++ b/libcap/cap_alloc.c
@@ -19,7 +19,6 @@ __attribute__((constructor (300))) static void _initialize_libcap(void)
     }
     cap_set_syscall(NULL, NULL);
     _binary_search(_cap_max_bits, cap_get_bound, 0, __CAP_MAXBITS, __CAP_BITS);
-    cap_proc_root("/proc");
 }
 
 cap_value_t cap_max_bits(void)
diff --git a/libcap/cap_test.c b/libcap/cap_test.c
index 2c068aa..b523091 100644
--- a/libcap/cap_test.c
+++ b/libcap/cap_test.c
@@ -171,7 +171,7 @@ static int test_alloc(void)
     }
 
     old_root = cap_proc_root("blah");
-    if (old_root == NULL || strcmp(old_root, "/proc") != 0) {
+    if (old_root != NULL) {
 	printf("bad initial proc_root [%s]\n", old_root);
 	fflush(stdout);
 	retval = -1;
diff --git a/libcap/cap_text.c b/libcap/cap_text.c
index 1004aae..40bd59a 100644
--- a/libcap/cap_text.c
+++ b/libcap/cap_text.c
@@ -669,7 +669,7 @@ static __u32 _parse_vec_string(__u32 *vals, const char *c, int invert)
 
 /*
  * libcap believes this is the root of the mounted "/proc"
- * filesystem
+ * filesystem. (NULL == "/proc".)
  */
 static char *_cap_proc_dir;
 
@@ -695,6 +695,8 @@ __attribute__((destructor (300))) static void _cleanup_libcap(void)
  * memory for storing the replacement root, and it is this memory that
  * is returned. So, when changing the value, the caller should
  * cap_free(the-return-value) when done with it.
+ *
+ * A return value of NULL implies the default is in effect "/proc".
  */
 char *cap_proc_root(const char *root)
 {
@@ -717,8 +719,12 @@ cap_iab_t cap_iab_get_pid(pid_t pid)
     char *path;
     FILE *file;
     char line[PROC_LINE_MAX];
+    const char *proc_root = _cap_proc_dir;
 
-    if (asprintf(&path, "%s/%d/status", _cap_proc_dir, pid) <= 0) {
+    if (proc_root == NULL) {
+	proc_root = "/proc";
+    }
+    if (asprintf(&path, "%s/%d/status", proc_root, pid) <= 0) {
 	return NULL;
     }
     file = fopen(path, "r");
diff --git a/libcap/include/sys/capability.h b/libcap/include/sys/capability.h
index 59f9377..80171b0 100644
--- a/libcap/include/sys/capability.h
+++ b/libcap/include/sys/capability.h
@@ -55,8 +55,9 @@ extern cap_value_t cap_max_bits(void);
 
 /*
  * cap_proc_root reads and (optionally: when root != NULL) changes
- * libcap's notion of where the "/proc" filesystem is mounted. It
- * defaults to the value "/proc".
+ * libcap's notion of where the "/proc" filesystem is mounted. When
+ * the return value is NULL, it should be interpreted as the
+ * value "/proc".
  *
  * Note, this is a global value and not considered thread safe to
  * write - so the client should take suitable care when changing
@@ -65,7 +66,10 @@ extern cap_value_t cap_max_bits(void);
  * Further, libcap will allocate a memory copy for storing the
  * replacement root, and it is this kind of memory that is returned.
  * So, when changing the value, the caller should
- * cap_free(the-return-value) when done with it.
+ * cap_free(the-return-value) else cause a memory leak.
+ *
+ * Note, the library uses a destructor to clean up the live allocated
+ * value of the working setting.
  */
 extern char *cap_proc_root(const char *root);