Fix raw_fallocate for Android and deal with unsupported filesystems.

io/include/pcl/io/low_level_io.h

@@ -60,6 +60,7 @@ typedef SSIZE_T ssize_t;
 # include <sys/types.h>
 # include <sys/stat.h>
 # include <sys/fcntl.h>
+# include <cerrno>
 #endif
 
 namespace pcl
@@ -97,10 +98,16 @@ namespace pcl
       return ::_write(fd, buffer, count);
     }
 
-    inline int raw_fallocate(int fd, long len)
+    inline int raw_ftruncate(int fd, long length)
     {
       return ::_chsize(fd, len);
     }
+
+    inline int raw_fallocate(int fd, long len)
+    {
+      // Doesn't actually allocate, but best we can do?
+      return raw_ftruncate(fd, len);
+    }
 #else
     inline int raw_open(const char * pathname, int flags, int mode)
     {
@@ -132,32 +139,75 @@ namespace pcl
       return ::write(fd, buffer, count);
     }
 
-# ifndef __APPLE__
-    inline int raw_fallocate(int fd, off_t len)
+    inline int raw_ftruncate(int fd, off_t length)
     {
-      return ::posix_fallocate(fd, 0, len);
+      return ::ftruncate(fd, length);
     }
-# else
+
+# ifdef __APPLE__
     inline int raw_fallocate(int fd, off_t len)
     {
+      // OS X doesn't have posix_fallocate, but it has a fcntl that does the job.
+      // It may make the file too big though, so we truncate before returning.
+
       // Try to allocate contiguous space first.
       ::fstore_t store = {F_ALLOCATEALL | F_ALLOCATECONTIG, F_PEOFPOSMODE, 0, len};
-      if (::fcntl(fd, F_PREALLOCATE, &store) < 0)
-      {
-        // Try fragmented if that failed.
-        store.fst_flags = F_ALLOCATEALL;
-        int ret = ::fcntl(fd, F_PREALLOCATE, &store);
-
-        // Bail if it still failed.
-        if (ret < 0) {
-          return ret;
-        }
-      }
-
-      // File could be larger than requested, so truncate.
-      return ::ftruncate(fd, len);
-    }
-# endif // __APPLE__
+      if (::fcntl(fd, F_PREALLOCATE, &store) != -1)
+        return raw_ftruncate(fd, len);
+
+      // Try fragmented if it failed.
+      store.fst_flags = F_ALLOCATEALL;
+      if (::fcntl(fd, F_PREALLOCATE, &store) != -1)
+        return raw_ftruncate(fd, len);
+
+      // Fragmented also failed.
+      return -1;
+    }
+
+# else // __APPLE__
+    inline int raw_fallocate(int fd, off_t len)
+    {
+#  ifdef ANDROID
+      // Android's libc doesn't have posix_fallocate.
+      if (::fallocate(fd, 0, 0, len) == 0)
+        return 0;
+#  else
+      // Conforming POSIX systems have posix_fallocate.
+      if (::posix_fallocate(fd, 0, len) == 0)
+        return 0;
+#  endif
+
+      // EINVAL should indicate an unsupported filesystem.
+      // All other errors are passed up.
+      if (errno != EINVAL)
+        return -1;
+
+      // Try to deal with unsupported filesystems by simply seeking + writing.
+      // This may not really allocate space, but the file size will be set.
+      // Writes to the mmapped file may still trigger SIGBUS errors later.
+
+      // Remember the old position and seek to the desired length.
+      off_t old_pos = raw_lseek(fd, 0, SEEK_CUR);
+      if (old_pos == -1)
+        return -1;
+      if (raw_lseek(fd, len - 1, SEEK_SET) == -1)
+        return -1;
+
+      // Write a single byte to resize the file.
+      char buffer = 0;
+      ssize_t written = raw_write(fd, &buffer, 1);
+
+      // Seek back to the old position.
+      if (raw_lseek(fd, old_pos, SEEK_SET) == -1)
+        return -1;
+
+      // Fail if we didn't write exactly one byte,
+      if (written != 1)
+        return -1;
+
+      return 0;
+    }
+# endif // __APPLE
 #endif // _WIN32
 
   }