Cygwin: sparse support: enable automatic sparsifying of files on SSDs

Given that SSDs don't have a seek penalty, we can enable
automatic sparsifying of files on SSDs, even if the "sparse"
mount option is not set.

Signed-off-by: Corinna Vinschen <corinna@vinschen.de>

winsup/cygwin/local_includes/path.h

@@ -174,8 +174,8 @@ class path_conv
   bool isgood_inode (ino_t ino) const;
   bool support_sparse () const
   {
-    return (mount_flags & MOUNT_SPARSE)
-	   && (fs_flags () & FILE_SUPPORTS_SPARSE_FILES);
+    return (fs_flags () & FILE_SUPPORTS_SPARSE_FILES)
+	   && (fs.is_ssd () || (mount_flags & MOUNT_SPARSE));
   }
   int has_dos_filenames_only () const {return mount_flags & MOUNT_DOS;}
   int has_buggy_reopen () const {return fs.has_buggy_reopen ();}

winsup/cygwin/release/3.5.0

@@ -55,3 +55,6 @@ What changed:
   https://www.austingroupbugs.net/view.php?id=1674
 
 - FIFOs now also work over NFS.
+
+- Enable automatic sparsifying of files on SSDs, independent of the
+  "sparse" mount mode.

winsup/doc/new-features.xml

@@ -82,6 +82,11 @@ New API call: fallocate (Linux-specific).
 FIFOs now also work over NFS.
 </para></listitem>
 
+<listitem><para>
+Enable automatic sparsifying of files on SSDs, independent of the
+"sparse" mount mode.
+</para></listitem>
+
 </itemizedlist>
 
 </sect2>

winsup/doc/utils.xml

@@ -1933,6 +1933,7 @@ D: on /d type fat (binary,user,noumount)
                (default).
   sparse     - Switch on support for sparse files.  This option only makes
                sense on NTFS and then only if you really need sparse files.
+	       This flag is always silently enabled on SSD drives.
   text       - Files default to CRLF text mode line endings.
 </screen>