If a file system supports uncached buffered IO, it may set FOP_DONTCACHE
and enable support for RWF_DONTCACHE. If RWF_DONTCACHE is attempted
without the file system supporting it, it'll get errored with -EOPNOTSUPP.
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
---
include/linux/fs.h | 14 +++++++++++++-
include/uapi/linux/fs.h | 6 +++++-
2 files changed, 18 insertions(+), 2 deletions(-)
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 7e29433c5ecc..6a838b5479a6 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -322,6 +322,7 @@ struct readahead_control;
#define IOCB_NOWAIT (__force int) RWF_NOWAIT
#define IOCB_APPEND (__force int) RWF_APPEND
#define IOCB_ATOMIC (__force int) RWF_ATOMIC
+#define IOCB_DONTCACHE (__force int) RWF_DONTCACHE
/* non-RWF related bits - start at 16 */
#define IOCB_EVENTFD (1 << 16)
@@ -356,7 +357,8 @@ struct readahead_control;
{ IOCB_SYNC, "SYNC" }, \
{ IOCB_NOWAIT, "NOWAIT" }, \
{ IOCB_APPEND, "APPEND" }, \
- { IOCB_ATOMIC, "ATOMIC"}, \
+ { IOCB_ATOMIC, "ATOMIC" }, \
+ { IOCB_DONTCACHE, "DONTCACHE" }, \
{ IOCB_EVENTFD, "EVENTFD"}, \
{ IOCB_DIRECT, "DIRECT" }, \
{ IOCB_WRITE, "WRITE" }, \
@@ -2127,6 +2129,8 @@ struct file_operations {
#define FOP_UNSIGNED_OFFSET ((__force fop_flags_t)(1 << 5))
/* Supports asynchronous lock callbacks */
#define FOP_ASYNC_LOCK ((__force fop_flags_t)(1 << 6))
+/* File system supports uncached read/write buffered IO */
+#define FOP_DONTCACHE ((__force fop_flags_t)(1 << 7))
/* Wrap a directory iterator that needs exclusive inode access */
int wrap_directory_iterator(struct file *, struct dir_context *,
@@ -3614,6 +3618,14 @@ static inline int kiocb_set_rw_flags(struct kiocb *ki, rwf_t flags,
if (!(ki->ki_filp->f_mode & FMODE_CAN_ATOMIC_WRITE))
return -EOPNOTSUPP;
}
+ if (flags & RWF_DONTCACHE) {
+ /* file system must support it */
+ if (!(ki->ki_filp->f_op->fop_flags & FOP_DONTCACHE))
+ return -EOPNOTSUPP;
+ /* DAX mappings not supported */
+ if (IS_DAX(ki->ki_filp->f_mapping->host))
+ return -EOPNOTSUPP;
+ }
kiocb_flags |= (__force int) (flags & RWF_SUPPORTED);
if (flags & RWF_SYNC)
kiocb_flags |= IOCB_DSYNC;
diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h
index 753971770733..56a4f93a08f4 100644
--- a/include/uapi/linux/fs.h
+++ b/include/uapi/linux/fs.h
@@ -332,9 +332,13 @@ typedef int __bitwise __kernel_rwf_t;
/* Atomic Write */
#define RWF_ATOMIC ((__force __kernel_rwf_t)0x00000040)
+/* buffered IO that drops the cache after reading or writing data */
+#define RWF_DONTCACHE ((__force __kernel_rwf_t)0x00000080)
+
/* mask of flags supported by the kernel */
#define RWF_SUPPORTED (RWF_HIPRI | RWF_DSYNC | RWF_SYNC | RWF_NOWAIT |\
- RWF_APPEND | RWF_NOAPPEND | RWF_ATOMIC)
+ RWF_APPEND | RWF_NOAPPEND | RWF_ATOMIC |\
+ RWF_DONTCACHE)
#define PROCFS_IOCTL_MAGIC 'f'
--
2.45.2
