[res] Don't stat asset providers on RO filesystems

IsUpToDate() is one of the most often called functions, let's
make sure it only performs a syscall if it makes any sense and
the underlying file can really change.

Bug: 237583012
Test: build + boot + UTs
Change-Id: Ie5999ddadf10b56f35354d00ad3402b229ffa2c3

3 files changed, 72 insertions, 23 deletions

diff --git a/libs/androidfw/AssetsProvider.cpp b/libs/androidfw/AssetsProvider.cpp
index 24460a4c0867..b9264c5d0f2d 100644
--- a/libs/androidfw/AssetsProvider.cpp
+++ b/libs/androidfw/AssetsProvider.cpp
@@ -104,12 +104,15 @@ std::unique_ptr<ZipAssetsProvider> ZipAssetsProvider::Create(std::string path,
   }
 
   struct stat sb{.st_mtime = -1};
-  if ((released_fd < 0 ? stat(path.c_str(), &sb) : fstat(released_fd, &sb)) < 0) {
-    // Stat requires execute permissions on all directories path to the file. If the process does
-    // not have execute permissions on this file, allow the zip to be opened but IsUpToDate() will
-    // always have to return true.
-    LOG(WARNING) << "Failed to stat file '" << path << "': "
-                 << base::SystemErrorCodeToString(errno);
+  // Skip all up-to-date checks if the file won't ever change.
+  if (!isReadonlyFilesystem(path.c_str())) {
+    if ((released_fd < 0 ? stat(path.c_str(), &sb) : fstat(released_fd, &sb)) < 0) {
+      // Stat requires execute permissions on all directories path to the file. If the process does
+      // not have execute permissions on this file, allow the zip to be opened but IsUpToDate() will
+      // always have to return true.
+      LOG(WARNING) << "Failed to stat file '" << path << "': "
+                   << base::SystemErrorCodeToString(errno);
+    }
   }
 
   return std::unique_ptr<ZipAssetsProvider>(
@@ -136,12 +139,15 @@ std::unique_ptr<ZipAssetsProvider> ZipAssetsProvider::Create(base::unique_fd fd,
   }
 
   struct stat sb{.st_mtime = -1};
-  if (fstat(released_fd, &sb) < 0) {
-    // Stat requires execute permissions on all directories path to the file. If the process does
-    // not have execute permissions on this file, allow the zip to be opened but IsUpToDate() will
-    // always have to return true.
-    LOG(WARNING) << "Failed to fstat file '" << friendly_name << "': "
-                 << base::SystemErrorCodeToString(errno);
+  // Skip all up-to-date checks if the file won't ever change.
+  if (!isReadonlyFilesystem(released_fd)) {
+    if (fstat(released_fd, &sb) < 0) {
+      // Stat requires execute permissions on all directories path to the file. If the process does
+      // not have execute permissions on this file, allow the zip to be opened but IsUpToDate() will
+      // always have to return true.
+      LOG(WARNING) << "Failed to fstat file '" << friendly_name
+                   << "': " << base::SystemErrorCodeToString(errno);
+    }
   }
 
   return std::unique_ptr<ZipAssetsProvider>(
@@ -278,6 +284,9 @@ const std::string& ZipAssetsProvider::GetDebugName() const {
 }
 
 bool ZipAssetsProvider::IsUpToDate() const {
+  if (last_mod_time_ == -1) {
+    return true;
+  }
   struct stat sb{};
   if (fstat(GetFileDescriptor(zip_handle_.get()), &sb) < 0) {
     // If fstat fails on the zip archive, return true so the zip archive the resource system does
@@ -291,7 +300,7 @@ DirectoryAssetsProvider::DirectoryAssetsProvider(std::string&& path, time_t last
     : dir_(std::forward<std::string>(path)), last_mod_time_(last_mod_time) {}
 
 std::unique_ptr<DirectoryAssetsProvider> DirectoryAssetsProvider::Create(std::string path) {
-  struct stat sb{};
+  struct stat sb;
   const int result = stat(path.c_str(), &sb);
   if (result == -1) {
     LOG(ERROR) << "Failed to find directory '" << path << "'.";
@@ -307,8 +316,9 @@ std::unique_ptr<DirectoryAssetsProvider> DirectoryAssetsProvider::Create(std::st
     path += OS_PATH_SEPARATOR;
   }
 
-  return std::unique_ptr<DirectoryAssetsProvider>(new DirectoryAssetsProvider(std::move(path),
-                                                                              sb.st_mtime));
+  const bool isReadonly = isReadonlyFilesystem(path.c_str());
+  return std::unique_ptr<DirectoryAssetsProvider>(
+      new DirectoryAssetsProvider(std::move(path), isReadonly ? -1 : sb.st_mtime));
 }
 
 std::unique_ptr<Asset> DirectoryAssetsProvider::OpenInternal(const std::string& path,
@@ -338,7 +348,10 @@ const std::string& DirectoryAssetsProvider::GetDebugName() const {
 }
 
 bool DirectoryAssetsProvider::IsUpToDate() const {
-  struct stat sb{};
+  if (last_mod_time_ == -1) {
+    return true;
+  }
+  struct stat sb;
   if (stat(dir_.c_str(), &sb) < 0) {
     // If stat fails on the zip archive, return true so the zip archive the resource system does
     // attempt to refresh the ApkAsset.
@@ -434,4 +447,4 @@ bool EmptyAssetsProvider::IsUpToDate() const {
   return true;
 }
 
-} // namespace android
\ No newline at end of file
+} // namespace android
diff --git a/libs/androidfw/include/androidfw/misc.h b/libs/androidfw/include/androidfw/misc.h
index 5a5a0e29125d..d40d24ede769 100644
--- a/libs/androidfw/include/androidfw/misc.h
+++ b/libs/androidfw/include/androidfw/misc.h
@@ -44,6 +44,10 @@ FileType getFileType(const char* fileName);
 /* get the file's modification date; returns -1 w/errno set on failure */
 time_t getFileModDate(const char* fileName);
 
+// Check if |path| or |fd| resides on a readonly filesystem.
+bool isReadonlyFilesystem(const char* path);
+bool isReadonlyFilesystem(int fd);
+
 }; // namespace android
 
 #endif // _LIBS_ANDROID_FW_MISC_H
diff --git a/libs/androidfw/misc.cpp b/libs/androidfw/misc.cpp
index 52854205207c..7af506638ebc 100644
--- a/libs/androidfw/misc.cpp
+++ b/libs/androidfw/misc.cpp
@@ -21,12 +21,17 @@
 //
 #include <androidfw/misc.h>
 
-#include <sys/stat.h>
+#include "android-base/logging.h"
+
+#ifndef _WIN32
+#include <sys/statvfs.h>
+#include <sys/vfs.h>
+#endif  // _WIN32
+
 #include <cstring>
-#include <errno.h>
 #include <cstdio>
-
-using namespace android;
+#include <errno.h>
+#include <sys/stat.h>
 
 namespace android {
 
@@ -41,8 +46,7 @@ FileType getFileType(const char* fileName)
         if (errno == ENOENT || errno == ENOTDIR)
             return kFileTypeNonexistent;
         else {
-            fprintf(stderr, "getFileType got errno=%d on '%s'\n",
-                errno, fileName);
+            PLOG(ERROR) << "getFileType(): stat(" << fileName << ") failed";
             return kFileTypeUnknown;
         }
     } else {
@@ -82,4 +86,32 @@ time_t getFileModDate(const char* fileName)
     return sb.st_mtime;
 }
 
+#ifdef _WIN32
+// No need to implement these for Windows, the functions only matter on a device.
+bool isReadonlyFilesystem(const char*) {
+    return false;
+}
+bool isReadonlyFilesystem(int) {
+    return false;
+}
+#else   // _WIN32
+bool isReadonlyFilesystem(const char* path) {
+    struct statfs sfs;
+    if (::statfs(path, &sfs)) {
+        PLOG(ERROR) << "isReadonlyFilesystem(): statfs(" << path << ") failed";
+        return false;
+    }
+    return (sfs.f_flags & ST_RDONLY) != 0;
+}
+
+bool isReadonlyFilesystem(int fd) {
+    struct statfs sfs;
+    if (::fstatfs(fd, &sfs)) {
+        PLOG(ERROR) << "isReadonlyFilesystem(): fstatfs(" << fd << ") failed";
+        return false;
+    }
+    return (sfs.f_flags & ST_RDONLY) != 0;
+}
+#endif  // _WIN32
+
 }; // namespace android