Added ashmem_get_size_region() function.

This is needed by the MemoryFile changes in
https://android-git.corp.google.com/g/2714
where it is used to find out whether a file descriptor
refers to an ashmem region.

3 files changed, 26 insertions, 0 deletions

diff --git a/include/cutils/ashmem.h b/include/cutils/ashmem.h
index fd71352..0683bf2 100644
--- a/include/cutils/ashmem.h
+++ b/include/cutils/ashmem.h
@@ -18,6 +18,7 @@ int ashmem_create_region(const char *name, size_t size);
 int ashmem_set_prot_region(int fd, int prot);
 int ashmem_pin_region(int fd, size_t offset, size_t len);
 int ashmem_unpin_region(int fd, size_t offset, size_t len);
+int ashmem_get_size_region(int fd);
 
 #ifdef __cplusplus
 }
diff --git a/libcutils/ashmem-dev.c b/libcutils/ashmem-dev.c
index 5e158af..8b71f87 100644
--- a/libcutils/ashmem-dev.c
+++ b/libcutils/ashmem-dev.c
@@ -83,3 +83,8 @@ int ashmem_unpin_region(int fd, size_t offset, size_t len)
 	struct ashmem_pin pin = { offset, len };
 	return ioctl(fd, ASHMEM_UNPIN, &pin);
 }
+
+int ashmem_get_size_region(int fd)
+{
+  return ioctl(fd, ASHMEM_GET_SIZE, NULL);
+}
diff --git a/libcutils/ashmem-host.c b/libcutils/ashmem-host.c
index dbb52bc..f03e130 100644
--- a/libcutils/ashmem-host.c
+++ b/libcutils/ashmem-host.c
@@ -92,3 +92,23 @@ int ashmem_unpin_region(int fd, size_t offset, size_t len)
 {
 	return ASHMEM_IS_UNPINNED;
 }
+
+int ashmem_get_size_region(int fd)
+{
+        struct stat buf;
+        int result;
+
+        result = fstat(fd, &buf);
+        if (result == -1) {
+                return -1;
+        }
+
+        // Check if this is an "ashmem" region.
+        // TODO: This is very hacky, and can easily break. We need some reliable indicator.
+        if (!(buf.st_nlink == 0 && S_ISREG(buf.st_mode))) {
+                errno = ENOTTY;
+                return -1;
+        }
+
+        return (int)buf.st_size;  // TODO: care about overflow (> 2GB file)?
+}