truncate: new helpers

Introduce new truncate helpers truncate_pagecache and inode_newsize_ok.
vmtruncate is also consolidated from mm/memory.c and mm/nommu.c and
into mm/truncate.c.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Nick Piggin <npiggin@suse.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

5 files changed, 70 insertions, 102 deletions

diff --git a/mm/filemap.c b/mm/filemap.c
index bcc7372aebbc..33349adb227a 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -58,7 +58,7 @@
 /*
  * Lock ordering:
  *
- *  ->i_mmap_lock               (vmtruncate)
+ *  ->i_mmap_lock               (truncate_pagecache)
  *    ->private_lock            (__free_pte->__set_page_dirty_buffers)
  *      ->swap_lock             (exclusive_swap_page, others)
  *        ->mapping->tree_lock
diff --git a/mm/memory.c b/mm/memory.c
index b1443ac07c00..ebcd3decac89 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -297,7 +297,8 @@ void free_pgtables(struct mmu_gather *tlb, struct vm_area_struct *vma,
                 unsigned long addr = vma->vm_start;
 
                 /*
-                 * Hide vma from rmap and vmtruncate before freeing pgtables
+                 * Hide vma from rmap and truncate_pagecache before freeing
+                 * pgtables
                  */
                 anon_vma_unlink(vma);
                 unlink_file_vma(vma);
@@ -2407,7 +2408,7 @@ restart:
  * @mapping: the address space containing mmaps to be unmapped.
  * @holebegin: byte in first page to unmap, relative to the start of
  * the underlying file.  This will be rounded down to a PAGE_SIZE
- * boundary.  Note that this is different from vmtruncate(), which
+ * boundary.  Note that this is different from truncate_pagecache(), which
  * must keep the partial page.  In contrast, we must get rid of
  * partial pages.
  * @holelen: size of prospective hole in bytes.  This will be rounded
@@ -2458,63 +2459,6 @@ void unmap_mapping_range(struct address_space *mapping,
 }
 EXPORT_SYMBOL(unmap_mapping_range);
 
-/**
- * vmtruncate - unmap mappings "freed" by truncate() syscall
- * @inode: inode of the file used
- * @offset: file offset to start truncating
- *
- * NOTE! We have to be ready to update the memory sharing
- * between the file and the memory map for a potential last
- * incomplete page.  Ugly, but necessary.
- */
-int vmtruncate(struct inode * inode, loff_t offset)
-{
-        if (inode->i_size < offset) {
-                unsigned long limit;
-
-                limit = current->signal->rlim[RLIMIT_FSIZE].rlim_cur;
-                if (limit != RLIM_INFINITY && offset > limit)
-                        goto out_sig;
-                if (offset > inode->i_sb->s_maxbytes)
-                        goto out_big;
-                i_size_write(inode, offset);
-        } else {
-                struct address_space *mapping = inode->i_mapping;
-
-                /*
-                 * truncation of in-use swapfiles is disallowed - it would
-                 * cause subsequent swapout to scribble on the now-freed
-                 * blocks.
-                 */
-                if (IS_SWAPFILE(inode))
-                        return -ETXTBSY;
-                i_size_write(inode, offset);
-
-                /*
-                 * unmap_mapping_range is called twice, first simply for
-                 * efficiency so that truncate_inode_pages does fewer
-                 * single-page unmaps.  However after this first call, and
-                 * before truncate_inode_pages finishes, it is possible for
-                 * private pages to be COWed, which remain after
-                 * truncate_inode_pages finishes, hence the second
-                 * unmap_mapping_range call must be made for correctness.
-                 */
-                unmap_mapping_range(mapping, offset + PAGE_SIZE - 1, 0, 1);
-                truncate_inode_pages(mapping, offset);
-                unmap_mapping_range(mapping, offset + PAGE_SIZE - 1, 0, 1);
-        }
-
-        if (inode->i_op->truncate)
-                inode->i_op->truncate(inode);
-        return 0;
-
-out_sig:
-        send_sig(SIGXFSZ, current, 0);
-out_big:
-        return -EFBIG;
-}
-EXPORT_SYMBOL(vmtruncate);
-
 int vmtruncate_range(struct inode *inode, loff_t offset, loff_t end)
 {
         struct address_space *mapping = inode->i_mapping;
diff --git a/mm/mremap.c b/mm/mremap.c
index 20a07dba6be0..97bff2547719 100644
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -86,8 +86,8 @@ static void move_ptes(struct vm_area_struct *vma, pmd_t *old_pmd,
         if (vma->vm_file) {
                 /*
                  * Subtle point from Rajesh Venkatasubramanian: before
-                 * moving file-based ptes, we must lock vmtruncate out,
-                 * since it might clean the dst vma before the src vma,
+                 * moving file-based ptes, we must lock truncate_pagecache
+                 * out, since it might clean the dst vma before the src vma,
                  * and we propagate stale pages into the dst afterward.
                  */
                 mapping = vma->vm_file->f_mapping;
diff --git a/mm/nommu.c b/mm/nommu.c
index 8d484241d034..56a446f05971 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -83,46 +83,6 @@ struct vm_operations_struct generic_file_vm_ops = {
 };
 
 /*
- * Handle all mappings that got truncated by a "truncate()"
- * system call.
- *
- * NOTE! We have to be ready to update the memory sharing
- * between the file and the memory map for a potential last
- * incomplete page.  Ugly, but necessary.
- */
-int vmtruncate(struct inode *inode, loff_t offset)
-{
-        struct address_space *mapping = inode->i_mapping;
-        unsigned long limit;
-
-        if (inode->i_size < offset)
-                goto do_expand;
-        i_size_write(inode, offset);
-
-        truncate_inode_pages(mapping, offset);
-        goto out_truncate;
-
-do_expand:
-        limit = current->signal->rlim[RLIMIT_FSIZE].rlim_cur;
-        if (limit != RLIM_INFINITY && offset > limit)
-                goto out_sig;
-        if (offset > inode->i_sb->s_maxbytes)
-                goto out;
-        i_size_write(inode, offset);
-
-out_truncate:
-        if (inode->i_op->truncate)
-                inode->i_op->truncate(inode);
-        return 0;
-out_sig:
-        send_sig(SIGXFSZ, current, 0);
-out:
-        return -EFBIG;
-}
-
-EXPORT_SYMBOL(vmtruncate);
-
-/*
  * Return the total memory allocated for this pointer, not
  * just what the caller asked for.
  *
diff --git a/mm/truncate.c b/mm/truncate.c
index ccc3ecf7cb98..5900afca0fa9 100644
--- a/mm/truncate.c
+++ b/mm/truncate.c
@@ -465,3 +465,67 @@ int invalidate_inode_pages2(struct address_space *mapping)
         return invalidate_inode_pages2_range(mapping, 0, -1);
 }
 EXPORT_SYMBOL_GPL(invalidate_inode_pages2);
+
+/**
+ * truncate_pagecache - unmap and remove pagecache that has been truncated
+ * @inode: inode
+ * @old: old file offset
+ * @new: new file offset
+ *
+ * inode's new i_size must already be written before truncate_pagecache
+ * is called.
+ *
+ * This function should typically be called before the filesystem
+ * releases resources associated with the freed range (eg. deallocates
+ * blocks). This way, pagecache will always stay logically coherent
+ * with on-disk format, and the filesystem would not have to deal with
+ * situations such as writepage being called for a page that has already
+ * had its underlying blocks deallocated.
+ */
+void truncate_pagecache(struct inode *inode, loff_t old, loff_t new)
+{
+        if (new < old) {
+                struct address_space *mapping = inode->i_mapping;
+
+                /*
+                 * unmap_mapping_range is called twice, first simply for
+                 * efficiency so that truncate_inode_pages does fewer
+                 * single-page unmaps.  However after this first call, and
+                 * before truncate_inode_pages finishes, it is possible for
+                 * private pages to be COWed, which remain after
+                 * truncate_inode_pages finishes, hence the second
+                 * unmap_mapping_range call must be made for correctness.
+                 */
+                unmap_mapping_range(mapping, new + PAGE_SIZE - 1, 0, 1);
+                truncate_inode_pages(mapping, new);
+                unmap_mapping_range(mapping, new + PAGE_SIZE - 1, 0, 1);
+        }
+}
+EXPORT_SYMBOL(truncate_pagecache);
+
+/**
+ * vmtruncate - unmap mappings "freed" by truncate() syscall
+ * @inode: inode of the file used
+ * @offset: file offset to start truncating
+ *
+ * NOTE! We have to be ready to update the memory sharing
+ * between the file and the memory map for a potential last
+ * incomplete page.  Ugly, but necessary.
+ */
+int vmtruncate(struct inode *inode, loff_t offset)
+{
+        loff_t oldsize;
+        int error;
+
+        error = inode_newsize_ok(inode, offset);
+        if (error)
+                return error;
+        oldsize = inode->i_size;
+        i_size_write(inode, offset);
+        truncate_pagecache(inode, oldsize, offset);
+        if (inode->i_op->truncate)
+                inode->i_op->truncate(inode);
+
+        return error;
+}
+EXPORT_SYMBOL(vmtruncate);