[RFC 6/8] ext4: Add an inode flag for atomic writes

["Ritesh Harjani (IBM)" <ritesh.list@gmail.com>]

This patch adds an inode atomic writes flag to ext4
(EXT4_ATOMICWRITES_FL which uses FS_ATOMICWRITES_FL flag).
Also add support for setting of this flag via ioctl.

Co-developed-by: Ojaswin Mujoo <ojaswin@linux.ibm.com>
Signed-off-by: Ojaswin Mujoo <ojaswin@linux.ibm.com>
Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
---
 fs/ext4/ext4.h  |  6 ++++++
 fs/ext4/ioctl.c | 11 +++++++++++
 2 files changed, 17 insertions(+)

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 1d2bce26e616..aa7fff2d6f96 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -495,8 +495,12 @@ struct flex_groups {
 #define EXT4_EA_INODE_FL	        0x00200000 /* Inode used for large EA */
 /* 0x00400000 was formerly EXT4_EOFBLOCKS_FL */
 
+#define EXT4_ATOMICWRITES_FL		FS_ATOMICWRITES_FL /* Inode supports atomic writes */
 #define EXT4_DAX_FL			0x02000000 /* Inode is DAX */
 
+/* 0x04000000 unused for now */
+/* 0x08000000 unused for now */
+
 #define EXT4_INLINE_DATA_FL		0x10000000 /* Inode has inline data. */
 #define EXT4_PROJINHERIT_FL		0x20000000 /* Create with parents projid */
 #define EXT4_CASEFOLD_FL		0x40000000 /* Casefolded directory */
@@ -519,6 +523,7 @@ struct flex_groups {
 					 0x00400000 /* EXT4_EOFBLOCKS_FL */ | \
 					 EXT4_DAX_FL | \
 					 EXT4_PROJINHERIT_FL | \
+					 EXT4_ATOMICWRITES_FL | \
 					 EXT4_CASEFOLD_FL)
 
 /* User visible flags */
@@ -593,6 +598,7 @@ enum {
 	EXT4_INODE_VERITY	= 20,	/* Verity protected inode */
 	EXT4_INODE_EA_INODE	= 21,	/* Inode used for large EA */
 /* 22 was formerly EXT4_INODE_EOFBLOCKS */
+	EXT4_INODE_ATOMIC_WRITE	= 24,	/* file does ATOMIC WRITE */
 	EXT4_INODE_DAX		= 25,	/* Inode is DAX */
 	EXT4_INODE_INLINE_DATA	= 28,	/* Data in inode. */
 	EXT4_INODE_PROJINHERIT	= 29,	/* Create with parents projid */
diff --git a/fs/ext4/ioctl.c b/fs/ext4/ioctl.c
index 7160a71044c8..03d0b501cbc8 100644
--- a/fs/ext4/ioctl.c
+++ b/fs/ext4/ioctl.c
@@ -632,6 +632,17 @@ static int ext4_ioctl_setflags(struct inode *inode,
 		}
 	}
 
+	if (flags & EXT4_ATOMICWRITES_FL) {
+		if (!ext4_can_atomic_write_fsawu(sb))
+			return -EOPNOTSUPP;
+
+		/* TODO: Do we need locks to check i_reserved_data_blocks */
+		if (!S_ISREG(inode->i_mode) || ext4_has_inline_data(inode) ||
+				READ_ONCE(ei->i_disksize) ||
+				EXT4_I(inode)->i_reserved_data_blocks)
+			return -EOPNOTSUPP;
+	}
+
 	/*
 	 * Wait for all pending directio and then flush all the dirty pages
 	 * for this file.  The flush marks all the pages readonly, so any
-- 
2.43.0