[PATCH] Add flag to files with blocks intentionally past EOF

[Eric Sandeen <sandeen@redhat.com>]

From: Jiaying Zhang <jiayingz@google.com>

fallocate() may potentially instantiate blocks past EOF, depending
on the flags used when it is called.

e2fsck currently has a test for blocks past i_size, and it
sometimes trips up - noticeably on xfstests 013 which runs fsstress.

This patch from Jiayang does fix it up for me - it (along with
e2fsprogs updates and other patches recently from Aneesh) has
survived many fsstress runs in a row.

The setattr interface may also be used to clear the flag and remove
any blocks past EOF.

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
---

(just resending this since it probably got lost in the previous
thread - Jiaying didn't have a SOB line, but maybe that should
be added.  I have included the proper From: line for authorship)

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 874d169..4c7cd9b 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -284,10 +284,11 @@ struct flex_groups {
 #define EXT4_TOPDIR_FL			0x00020000 /* Top of directory hierarchies*/
 #define EXT4_HUGE_FILE_FL               0x00040000 /* Set to each huge file */
 #define EXT4_EXTENTS_FL			0x00080000 /* Inode uses extents */
+#define EXT4_EOFBLOCKS_FL		0x00400000 /* Blocks allocated beyond EOF (bit reserved in fs.h) */
 #define EXT4_RESERVED_FL		0x80000000 /* reserved for ext4 lib */
 
-#define EXT4_FL_USER_VISIBLE		0x000BDFFF /* User visible flags */
-#define EXT4_FL_USER_MODIFIABLE		0x000B80FF /* User modifiable flags */
+#define EXT4_FL_USER_VISIBLE		0x004BDFFF /* User visible flags */
+#define EXT4_FL_USER_MODIFIABLE		0x004B80FF /* User modifiable flags */
 
 /* Flags that should be inherited by new inodes from their parent. */
 #define EXT4_FL_INHERITED (EXT4_SECRM_FL | EXT4_UNRM_FL | EXT4_COMPR_FL |\
diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index 765a482..e7d5ba2 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -3185,7 +3185,7 @@ int ext4_ext_get_blocks(handle_t *handle, struct inode *inode,
 {
 	struct ext4_ext_path *path = NULL;
 	struct ext4_extent_header *eh;
-	struct ext4_extent newex, *ex;
+	struct ext4_extent newex, *ex, *last_ex;
 	ext4_fsblk_t newblock;
 	int err = 0, depth, ret, cache_type;
 	unsigned int allocated = 0;
@@ -3366,6 +3366,14 @@ int ext4_ext_get_blocks(handle_t *handle, struct inode *inode,
 					EXT4_STATE_DIO_UNWRITTEN;;
 		}
 	}
+
+	if (unlikely(inode->i_flags & EXT4_EOFBLOCKS_FL)) {
+		BUG_ON(!eh->eh_entries);
+		last_ex = EXT_LAST_EXTENT(eh);
+		if (iblock + ar.len > le32_to_cpu(last_ex->ee_block)
+					+ ext4_ext_get_actual_len(last_ex))
+			inode->i_flags &= ~EXT4_EOFBLOCKS_FL;
+	}
 	err = ext4_ext_insert_extent(handle, inode, path, &newex, flags);
 	if (err) {
 		/* free data blocks we just allocated */
@@ -3499,6 +3507,13 @@ static void ext4_falloc_update_inode(struct inode *inode,
 			i_size_write(inode, new_size);
 		if (new_size > EXT4_I(inode)->i_disksize)
 			ext4_update_i_disksize(inode, new_size);
+	} else {
+		/*
+		 * Mark that we allocate beyond EOF so the subsequent truncate
+		 * can proceed even if the new size is the same as i_size.
+		 */
+		if (new_size > i_size_read(inode))
+			inode->i_flags |= EXT4_EOFBLOCKS_FL;
 	}
 
 }
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index cbf56da..bc31ea6 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -4429,6 +4429,8 @@ void ext4_truncate(struct inode *inode)
 	if (!ext4_can_truncate(inode))
 		return;
 
+	inode->i_flags &= ~EXT4_EOFBLOCKS_FL;
+
 	if (inode->i_size == 0 && !test_opt(inode->i_sb, NO_AUTO_DA_ALLOC))
 		ei->i_state |= EXT4_STATE_DA_ALLOC_CLOSE;
 
@@ -4741,8 +4743,8 @@ void ext4_get_inode_flags(struct ext4_inode_info *ei)
 {
 	unsigned int flags = ei->vfs_inode.i_flags;
 
-	ei->i_flags &= ~(EXT4_SYNC_FL|EXT4_APPEND_FL|
-			EXT4_IMMUTABLE_FL|EXT4_NOATIME_FL|EXT4_DIRSYNC_FL);
+	ei->i_flags &= ~(EXT4_SYNC_FL|EXT4_APPEND_FL|EXT4_IMMUTABLE_FL|
+			EXT4_NOATIME_FL|EXT4_DIRSYNC_FL|EXT4_EOFBLOCKS_FL);
 	if (flags & S_SYNC)
 		ei->i_flags |= EXT4_SYNC_FL;
 	if (flags & S_APPEND)
@@ -4753,6 +4755,8 @@ void ext4_get_inode_flags(struct ext4_inode_info *ei)
 		ei->i_flags |= EXT4_NOATIME_FL;
 	if (flags & S_DIRSYNC)
 		ei->i_flags |= EXT4_DIRSYNC_FL;
+	if (flags & FS_EOFBLOCKS_FL)
+		ei->i_flags |= EXT4_EOFBLOCKS_FL;
 }
 
 static blkcnt_t ext4_inode_blocks(struct ext4_inode *raw_inode,
@@ -5284,7 +5288,9 @@ int ext4_setattr(struct dentry *dentry, struct iattr *attr)
 	}
 
 	if (S_ISREG(inode->i_mode) &&
-	    attr->ia_valid & ATTR_SIZE && attr->ia_size < inode->i_size) {
+	    attr->ia_valid & ATTR_SIZE &&
+	    (attr->ia_size < inode->i_size ||
+	     (inode->i_flags & EXT4_EOFBLOCKS_FL))) {
 		handle_t *handle;
 
 		handle = ext4_journal_start(inode, 3);
@@ -5315,6 +5321,11 @@ int ext4_setattr(struct dentry *dentry, struct iattr *attr)
 				goto err_out;
 			}
 		}
+		if ((inode->i_flags & EXT4_EOFBLOCKS_FL)) {
+			rc = vmtruncate(inode, attr->ia_size);
+			if (rc)
+				goto err_out;
+		}
 	}
 
 	rc = inode_setattr(inode, attr);
diff --git a/fs/ext4/ioctl.c b/fs/ext4/ioctl.c
index b63d193..71f578e 100644
--- a/fs/ext4/ioctl.c
+++ b/fs/ext4/ioctl.c
@@ -92,6 +92,16 @@ long ext4_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 			flags &= ~EXT4_EXTENTS_FL;
 		}
 
+		if (flags & EXT4_EOFBLOCKS_FL) {
+			/* we don't support adding EOFBLOCKS flag */
+			if (!(oldflags & EXT4_EOFBLOCKS_FL)) {
+				err = -EOPNOTSUPP;
+				goto flags_out;
+			}
+		} else if (oldflags & EXT4_EOFBLOCKS_FL)
+			/* free the space reserved with fallocate KEEPSIZE */
+			vmtruncate(inode, inode->i_size);
+
 		handle = ext4_journal_start(inode, 1);
 		if (IS_ERR(handle)) {
 			err = PTR_ERR(handle);
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 9147ca8..db3ffb6 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -349,10 +349,11 @@ struct inodes_stat_t {
 #define FS_TOPDIR_FL			0x00020000 /* Top of directory hierarchies*/
 #define FS_EXTENT_FL			0x00080000 /* Extents */
 #define FS_DIRECTIO_FL			0x00100000 /* Use direct i/o */
+#define FS_EOFBLOCKS_FL			0x00400000 /* Blocks allocated beyond EOF */
 #define FS_RESERVED_FL			0x80000000 /* reserved for ext2 lib */
 
-#define FS_FL_USER_VISIBLE		0x0003DFFF /* User visible flags */
-#define FS_FL_USER_MODIFIABLE		0x000380FF /* User modifiable flags */
+#define FS_FL_USER_VISIBLE		0x0043DFFF /* User visible flags */
+#define FS_FL_USER_MODIFIABLE		0x004380FF /* User modifiable flags */
 
 
 #define SYNC_FILE_RANGE_WAIT_BEFORE	1