Introduce the 'usertemp' filesystem type

	* mount.cc (mount_info::from_fstab_line): Support mounting the current
	user's temp folder as /tmp/.  This is particularly useful a feature
	when Cygwin's own files are write-protected.

	* pathnames.xml: document the new usertemp file system type

Detailed explanation:

In the context of Windows, there is a per-user directory for temporary
files, by default specified via the environment variable %TEMP%. Let's
allow to use that directory for our /tmp/ directory.

With this patch, we introduce the special filesystem type "usertemp":
By specifying

	none /tmp usertemp binary,posix=0 0 0

in /etc/fstab, the /tmp/ directory gets auto-mounted to the directory
specified by the %TEMP% variable.

This feature comes handy in particularly in scenarios where the
administrator might want to write-protect the entire Cygwin directory
yet still needs to allow users to write into the /tmp/ directory.
This is the case in the context of Git for Windows, where the
Cygwin (MSys2) root directory lives inside C:\Program Files and hence
/tmp/ would not be writable otherwise.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

1 files changed, 21 insertions, 0 deletions

diff --git a/winsup/cygwin/mount.cc b/winsup/cygwin/mount.cc
index 68977fd58..df96c2dc2 100644
--- a/winsup/cygwin/mount.cc
+++ b/winsup/cygwin/mount.cc
@@ -1186,6 +1186,8 @@ mount_info::from_fstab_line (char *line, bool user)
   unsigned mount_flags = MOUNT_SYSTEM | MOUNT_BINARY;
   if (!strcmp (fs_type, "cygdrive"))
     mount_flags |= MOUNT_NOPOSIX;
+  if (!strcmp (fs_type, "usertemp"))
+    mount_flags |= MOUNT_IMMUTABLE;
   if (!fstab_read_flags (&c, mount_flags, false))
     return true;
   if (mount_flags & MOUNT_BIND)
@@ -1210,6 +1212,22 @@ mount_info::from_fstab_line (char *line, bool user)
       slashify (posix_path, cygdrive, 1);
       cygdrive_len = strlen (cygdrive);
     }
+  else if (!strcmp (fs_type, "usertemp"))
+    {
+      WCHAR tmp[PATH_MAX + 1];
+
+      if (GetTempPathW (PATH_MAX, tmp))
+	{
+	  tmp_pathbuf tp;
+	  char *mb_tmp = tp.c_get ();
+	  sys_wcstombs (mb_tmp, PATH_MAX, tmp);
+
+	  mount_flags |= MOUNT_USER_TEMP;
+	  int res = mount_table->add_item (mb_tmp, posix_path, mount_flags);
+	  if (res && get_errno () == EMFILE)
+	    return false;
+	}
+    }
   else
     {
       int res = mount_table->add_item (native_path, posix_path, mount_flags);
@@ -1667,6 +1685,9 @@ fillout_mntent (const char *native_path, const char *posix_path, unsigned flags)
   if (flags & (MOUNT_BIND))
     strcat (_my_tls.locals.mnt_opts, (char *) ",bind");
 
+  if (flags & (MOUNT_USER_TEMP))
+    strcat (_my_tls.locals.mnt_opts, (char *) ",usertemp");
+
   ret.mnt_opts = _my_tls.locals.mnt_opts;
 
   ret.mnt_freq = 1;