gistfile1.patch

commit c1e45e725b91bc4e03d7e3acc94673ea7b16d762
Author: Richard Braakman <richard.braakman@jollamobile.com>
Date:   Tue Jan 29 21:48:13 2013 +0200

    [vboxsf] support writable mmap
    
    This is mainly so that guest processes can use the shared folder as a backing
    for database files and such. Don't expect coherence if a file is simultaneously
    mmapped on the host and guest sides.

diff --git a/src/VBox/Additions/linux/sharedfolders/regops.c b/src/VBox/Additions/linux/sharedfolders/regops.c
index a0586bd..c3b314e 100644
--- a/src/VBox/Additions/linux/sharedfolders/regops.c
+++ b/src/VBox/Additions/linux/sharedfolders/regops.c
@@ -16,7 +16,7 @@
  */
 
 /*
- * Limitations: only COW memory mapping is supported
+ * Limitations: MAP_SHARED mmap does not notice changes made on the host.
  */
 
 #include "vfsmod.h"
@@ -501,7 +501,7 @@ static struct page *sf_reg_nopage(struct vm_area_struct *vma, unsigned long vadd
     /* Don't use GFP_HIGHUSER as long as sf_reg_read_aux() calls vboxCallRead()
      * which works on virtual addresses. On Linux cannot reliably determine the
      * physical address for high memory, see rtR0MemObjNativeLockKernel(). */
-    page = alloc_page(GFP_USER);
+    page = find_or_create_page(inode->i_mapping, vmf->pgoff, GFP_USER);
     if (!page) {
         LogRelFunc(("failed to allocate page\n"));
 #if LINUX_VERSION_CODE > KERNEL_VERSION(2, 6, 25)
@@ -522,7 +522,8 @@ static struct page *sf_reg_nopage(struct vm_area_struct *vma, unsigned long vadd
     if (err)
     {
         kunmap(page);
-        put_page(page);
+        unlock_page(page);
+        page_cache_release(page);
 #if LINUX_VERSION_CODE > KERNEL_VERSION(2, 6, 25)
         return VM_FAULT_SIGBUS;
 #else
@@ -546,7 +547,9 @@ static struct page *sf_reg_nopage(struct vm_area_struct *vma, unsigned long vadd
         memset(buf + nread, 0, PAGE_SIZE - nread);
 
     flush_dcache_page(page);
+    SetPageUptodate(page);
     kunmap(page);
+    unlock_page(page);
 #if LINUX_VERSION_CODE > KERNEL_VERSION(2, 6, 25)
     vmf->page = page;
     return 0;
@@ -556,24 +559,51 @@ static struct page *sf_reg_nopage(struct vm_area_struct *vma, unsigned long vadd
 #endif
 }
 
+/**
+ * Prepare for a mmap page to be made writable.
+ * Check that the page is still there, and lock it if necessary to keep it there.
+ * Part of MAP_SHARED support.
+ *
+ * @returns VM_FAULT_LOCKED if the page is ready, otherwise VM_FAULT_NOPAGE.
+ */
+static int sf_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
+{
+    struct page *page = vmf->page;
+    struct inode *inode = vma->vm_file->f_path.dentry->d_inode;
+    loff_t size;
+
+    TRACE();
+
+    lock_page(page);
+    size = i_size_read(inode);
+    if (page->mapping != inode->i_mapping || page_offset(page) > size)
+    {
+        /* file was truncated */
+        unlock_page(page);
+        return VM_FAULT_NOPAGE;
+    }
+
+    wait_on_page_writeback(page);
+    return VM_FAULT_LOCKED;
+}
+
 static struct vm_operations_struct sf_vma_ops =
 {
 #if LINUX_VERSION_CODE > KERNEL_VERSION(2, 6, 25)
-    .fault = sf_reg_fault
+    .fault = sf_reg_fault,
 #else
-     .nopage = sf_reg_nopage
+     .nopage = sf_reg_nopage,
 #endif
+    .page_mkwrite = sf_page_mkwrite
 };
 
 static int sf_reg_mmap(struct file *file, struct vm_area_struct *vma)
 {
-    TRACE();
-    if (vma->vm_flags & VM_SHARED)
-    {
-        LogFunc(("shared mmapping not available\n"));
-        return -EINVAL;
-    }
+    struct sf_reg_info *sf_r = file->private_data;
 
+    TRACE();
+    if (sf_r->createflags & SHFL_CF_ACCESS_APPEND)
+        return -EINVAL; /* can't simulate page operations */
     vma->vm_ops = &sf_vma_ops;
     return 0;
 }
@@ -701,8 +731,8 @@ sf_writepage(struct page *page, struct writeback_control *wbc)
         goto out;
     }
 
-    if (off > inode->i_size)
-        inode->i_size = off;
+    if (off + nwritten > inode->i_size)
+        inode->i_size = off + nwritten;
 
     if (PageError(page))
         ClearPageError(page);