Add support for ashmem-host for host Windows
Migrate to tmpfile and fileno for temp file operations. These calls are
supported on MinGW, and the temp files are automatically cleaned up.
A Windows variant of ashmem-host is needed to support CursorWindows on
host Windows.
In Windows, it is not possible to unlink an open file, so the nlink
check in ashmem_validate_stat must be made Unix-only.
Test: SQLiteDatabaseTest in Google3
Test: libcutils_test_static on Windows
Bug: 317884162
Change-Id: I7fc0f1f49406b01549b7f4d7e138cb3e4d79be72
diff --git a/libcutils/ashmem-host.cpp b/libcutils/ashmem-host.cpp
index 2ba1eb0..9003b76 100644
--- a/libcutils/ashmem-host.cpp
+++ b/libcutils/ashmem-host.cpp
@@ -17,10 +17,13 @@
#include <cutils/ashmem.h>
/*
- * Implementation of the user-space ashmem API for the simulator, which lacks
- * an ashmem-enabled kernel. See ashmem-dev.c for the real ashmem-based version.
+ * Implementation of the user-space ashmem API for the simulator, which lacks an
+ * ashmem-enabled kernel. See ashmem-dev.c for the real ashmem-based version. A
+ * disk-backed temp file is the best option that is consistently supported
+ * across all host platforms.
*/
+#include <android-base/unique_fd.h>
#include <errno.h>
#include <fcntl.h>
#include <limits.h>
@@ -31,8 +34,10 @@
#include <sys/types.h>
#include <time.h>
#include <unistd.h>
-
#include <utils/Compat.h>
+#include <memory>
+
+using android::base::unique_fd;
static bool ashmem_validate_stat(int fd, struct stat* buf) {
int result = fstat(fd, buf);
@@ -40,15 +45,20 @@
return false;
}
- /*
- * 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))) {
+ // Check if this is an ashmem region. Since there's no such thing on the host,
+ // we can't actually implement that. Check that it's at least a regular file.
+ if (!S_ISREG(buf->st_mode)) {
errno = ENOTTY;
return false;
}
+ // In Win32, unlike Unix, the temp file is not unlinked immediately after
+ // creation.
+#if !defined(_WIN32)
+ if (buf->st_nlink != 0) {
+ errno = ENOTTY;
+ return false;
+ }
+#endif
return true;
}
@@ -58,19 +68,24 @@
}
int ashmem_create_region(const char* /*ignored*/, size_t size) {
- char pattern[PATH_MAX];
- snprintf(pattern, sizeof(pattern), "/tmp/android-ashmem-%d-XXXXXXXXX", getpid());
- int fd = mkstemp(pattern);
- if (fd == -1) return -1;
+ // Files returned by tmpfile are automatically removed.
+ std::unique_ptr<FILE, decltype(&fclose)> tmp(tmpfile(), &fclose);
- unlink(pattern);
-
- if (TEMP_FAILURE_RETRY(ftruncate(fd, size)) == -1) {
- close(fd);
- return -1;
+ if (!tmp) {
+ return -1;
}
-
- return fd;
+ int fd = fileno(tmp.get());
+ if (fd == -1) {
+ return -1;
+ }
+ unique_fd dupfd = unique_fd(dup(fd));
+ if (dupfd == -1) {
+ return -1;
+ }
+ if (TEMP_FAILURE_RETRY(ftruncate(dupfd, size)) == -1) {
+ return -1;
+ }
+ return dupfd.release();
}
int ashmem_set_prot_region(int /*fd*/, int /*prot*/) {