ocfs2: shared writeable mmap

Implement cluster consistent shared writeable mappings using the
->page_mkwrite() callback.

Signed-off-by: Mark Fasheh <mark.fasheh@oracle.com>

1 files changed, 143 insertions, 24 deletions

diff --git a/fs/ocfs2/mmap.c b/fs/ocfs2/mmap.c
index af01158b39f5..d79aa12137d2 100644
--- a/fs/ocfs2/mmap.c
+++ b/fs/ocfs2/mmap.c
@@ -37,11 +37,29 @@
 
 #include "ocfs2.h"
 
+#include "aops.h"
 #include "dlmglue.h"
 #include "file.h"
 #include "inode.h"
 #include "mmap.h"
 
+static inline int ocfs2_vm_op_block_sigs(sigset_t *blocked, sigset_t *oldset)
+{
+        /* The best way to deal with signals in the vm path is
+         * to block them upfront, rather than allowing the
+         * locking paths to return -ERESTARTSYS. */
+        sigfillset(blocked);
+
+        /* We should technically never get a bad return value
+         * from sigprocmask */
+        return sigprocmask(SIG_BLOCK, blocked, oldset);
+}
+
+static inline int ocfs2_vm_op_unblock_sigs(sigset_t *oldset)
+{
+        return sigprocmask(SIG_SETMASK, oldset, NULL);
+}
+
 static struct page *ocfs2_nopage(struct vm_area_struct * area,
                                  unsigned long address,
                                  int *type)
@@ -53,14 +71,7 @@ static struct page *ocfs2_nopage(struct vm_area_struct * area,
         mlog_entry("(area=%p, address=%lu, type=%p)\n", area, address,
                    type);
 
-        /* The best way to deal with signals in this path is
-         * to block them upfront, rather than allowing the
-         * locking paths to return -ERESTARTSYS. */
-        sigfillset(&blocked);
-
-        /* We should technically never get a bad ret return
-         * from sigprocmask */
-        ret = sigprocmask(SIG_BLOCK, &blocked, &oldset);
+        ret = ocfs2_vm_op_block_sigs(&blocked, &oldset);
         if (ret < 0) {
                 mlog_errno(ret);
                 goto out;
@@ -68,7 +79,7 @@ static struct page *ocfs2_nopage(struct vm_area_struct * area,
 
         page = filemap_nopage(area, address, type);
 
-        ret = sigprocmask(SIG_SETMASK, &oldset, NULL);
+        ret = ocfs2_vm_op_unblock_sigs(&oldset);
         if (ret < 0)
                 mlog_errno(ret);
 out:
@@ -76,28 +87,136 @@ out:
         return page;
 }
 
-static struct vm_operations_struct ocfs2_file_vm_ops = {
-        .nopage = ocfs2_nopage,
-};
+static int __ocfs2_page_mkwrite(struct inode *inode, struct buffer_head *di_bh,
+                                struct page *page)
+{
+        int ret;
+        struct address_space *mapping = inode->i_mapping;
+        loff_t pos = page->index << PAGE_CACHE_SHIFT;
+        unsigned int len = PAGE_CACHE_SIZE;
+        pgoff_t last_index;
+        struct page *locked_page = NULL;
+        void *fsdata;
+        loff_t size = i_size_read(inode);
 
-int ocfs2_mmap(struct file *file, struct vm_area_struct *vma)
+        /*
+         * Another node might have truncated while we were waiting on
+         * cluster locks.
+         */
+        last_index = size >> PAGE_CACHE_SHIFT;
+        if (page->index > last_index) {
+                ret = -EINVAL;
+                goto out;
+        }
+
+        /*
+         * The i_size check above doesn't catch the case where nodes
+         * truncated and then re-extended the file. We'll re-check the
+         * page mapping after taking the page lock inside of
+         * ocfs2_write_begin_nolock().
+         */
+        if (!PageUptodate(page) || page->mapping != inode->i_mapping) {
+                ret = -EINVAL;
+                goto out;
+        }
+
+        /*
+         * Call ocfs2_write_begin() and ocfs2_write_end() to take
+         * advantage of the allocation code there. We pass a write
+         * length of the whole page (chopped to i_size) to make sure
+         * the whole thing is allocated.
+         *
+         * Since we know the page is up to date, we don't have to
+         * worry about ocfs2_write_begin() skipping some buffer reads
+         * because the "write" would invalidate their data.
+         */
+        if (page->index == last_index)
+                len = size & ~PAGE_CACHE_MASK;
+
+        ret = ocfs2_write_begin_nolock(mapping, pos, len, 0, &locked_page,
+                                       &fsdata, di_bh, page);
+        if (ret) {
+                if (ret != -ENOSPC)
+                        mlog_errno(ret);
+                goto out;
+        }
+
+        ret = ocfs2_write_end_nolock(mapping, pos, len, len, locked_page,
+                                     fsdata);
+        if (ret < 0) {
+                mlog_errno(ret);
+                goto out;
+        }
+        BUG_ON(ret != len);
+        ret = 0;
+out:
+        return ret;
+}
+
+static int ocfs2_page_mkwrite(struct vm_area_struct *vma, struct page *page)
 {
-        int ret = 0, lock_level = 0;
-        struct ocfs2_super *osb = OCFS2_SB(file->f_dentry->d_inode->i_sb);
+        struct inode *inode = vma->vm_file->f_path.dentry->d_inode;
+        struct buffer_head *di_bh = NULL;
+        sigset_t blocked, oldset;
+        int ret, ret2;
+
+        ret = ocfs2_vm_op_block_sigs(&blocked, &oldset);
+        if (ret < 0) {
+                mlog_errno(ret);
+                return ret;
+        }
+
+        /*
+         * The cluster locks taken will block a truncate from another
+         * node. Taking the data lock will also ensure that we don't
+         * attempt page truncation as part of a downconvert.
+         */
+        ret = ocfs2_meta_lock(inode, &di_bh, 1);
+        if (ret < 0) {
+                mlog_errno(ret);
+                goto out;
+        }
 
         /*
-         * Only support shared writeable mmap for local mounts which
-         * don't know about holes.
+         * The alloc sem should be enough to serialize with
+         * ocfs2_truncate_file() changing i_size as well as any thread
+         * modifying the inode btree.
          */
-        if ((!ocfs2_mount_local(osb) || ocfs2_sparse_alloc(osb)) &&
-            ((vma->vm_flags & VM_SHARED) || (vma->vm_flags & VM_MAYSHARE)) &&
-            ((vma->vm_flags & VM_WRITE) || (vma->vm_flags & VM_MAYWRITE))) {
-                mlog(0, "disallow shared writable mmaps %lx\n", vma->vm_flags);
-                /* This is -EINVAL because generic_file_readonly_mmap
-                 * returns it in a similar situation. */
-                return -EINVAL;
+        down_write(&OCFS2_I(inode)->ip_alloc_sem);
+
+        ret = ocfs2_data_lock(inode, 1);
+        if (ret < 0) {
+                mlog_errno(ret);
+                goto out_meta_unlock;
         }
 
+        ret = __ocfs2_page_mkwrite(inode, di_bh, page);
+
+        ocfs2_data_unlock(inode, 1);
+
+out_meta_unlock:
+        up_write(&OCFS2_I(inode)->ip_alloc_sem);
+
+        brelse(di_bh);
+        ocfs2_meta_unlock(inode, 1);
+
+out:
+        ret2 = ocfs2_vm_op_unblock_sigs(&oldset);
+        if (ret2 < 0)
+                mlog_errno(ret2);
+
+        return ret;
+}
+
+static struct vm_operations_struct ocfs2_file_vm_ops = {
+        .nopage         = ocfs2_nopage,
+        .page_mkwrite   = ocfs2_page_mkwrite,
+};
+
+int ocfs2_mmap(struct file *file, struct vm_area_struct *vma)
+{
+        int ret = 0, lock_level = 0;
+
         ret = ocfs2_meta_lock_atime(file->f_dentry->d_inode,
                                     file->f_vfsmnt, &lock_level);
         if (ret < 0) {