[PATCH v4 1/6] fs: introduce FMODE_ZONE_APPEND and IOCB_ZONE_APPEND

[Kanchan Joshi <joshi.k@samsung.com>]

Enable zone-append using existing O_APPEND and RWF_APPEND.
Zone-append is similar to appending writes, but requires written-location
to be returned, in order to be effective.
Returning completion-result requires bit of additional processing in
common path. Also, we guarantee that zone-append does not cause a short
write, which is not the case with regular appending-write.
Therefore make the feature opt-in by introducing new FMODE_ZONE_APPEND
mode (kernel-only) and IOCB_ZONE_APPEND flag.
When a file is opened, it can opt in for zone-append by setting
FMODE_ZONE_APPEND.
If file has opted in, and receives write that meets file-append
criteria (RWF_APPEND write or O_APPEND open), set IOCB_ZONE_APPEND in
kiocb->ki_flag, apart from existing IOCB_APPEND. IOCB_ZONE_APPEND is
meant to isolate the code that returns written-location with appending
write.

Signed-off-by: Kanchan Joshi <joshi.k@samsung.com>
Signed-off-by: Selvakumar S <selvakuma.s1@samsung.com>
Signed-off-by: Nitesh Shetty <nj.shetty@samsung.com>
Signed-off-by: Javier Gonzalez <javier.gonz@samsung.com>
---
 include/linux/fs.h | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 6c4ab4d..ef13df4 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -175,6 +175,9 @@ typedef int (dio_iodone_t)(struct kiocb *iocb, loff_t offset,
 /* File does not contribute to nr_files count */
 #define FMODE_NOACCOUNT		((__force fmode_t)0x20000000)
 
+/* File can support zone-append */
+#define FMODE_ZONE_APPEND	((__force fmode_t)0x40000000)
+
 /*
  * Flag for rw_copy_check_uvector and compat_rw_copy_check_uvector
  * that indicates that they should check the contents of the iovec are
@@ -315,6 +318,7 @@ enum rw_hint {
 #define IOCB_SYNC		(1 << 5)
 #define IOCB_WRITE		(1 << 6)
 #define IOCB_NOWAIT		(1 << 7)
+#define IOCB_ZONE_APPEND	(1 << 8)
 
 struct kiocb {
 	struct file		*ki_filp;
@@ -3427,8 +3431,11 @@ static inline bool vma_is_fsdax(struct vm_area_struct *vma)
 static inline int iocb_flags(struct file *file)
 {
 	int res = 0;
-	if (file->f_flags & O_APPEND)
+	if (file->f_flags & O_APPEND) {
 		res |= IOCB_APPEND;
+		if (file->f_mode & FMODE_ZONE_APPEND)
+			res |= IOCB_ZONE_APPEND;
+	}
 	if (file->f_flags & O_DIRECT)
 		res |= IOCB_DIRECT;
 	if ((file->f_flags & O_DSYNC) || IS_SYNC(file->f_mapping->host))
@@ -3454,8 +3461,11 @@ static inline int kiocb_set_rw_flags(struct kiocb *ki, rwf_t flags)
 		ki->ki_flags |= IOCB_DSYNC;
 	if (flags & RWF_SYNC)
 		ki->ki_flags |= (IOCB_DSYNC | IOCB_SYNC);
-	if (flags & RWF_APPEND)
+	if (flags & RWF_APPEND) {
 		ki->ki_flags |= IOCB_APPEND;
+		if (ki->ki_filp->f_mode & FMODE_ZONE_APPEND)
+			ki->ki_flags |= IOCB_ZONE_APPEND;
+	}
 	return 0;
 }
 
-- 
2.7.4