[PATCH 07/17] fs: add RWF_UNCACHED iocb and FOP_UNCACHED file_operations flag

Jens Axboe
2024-11-14T15:28:12Z

If a file system supports uncached buffered IO, it may set FOP_UNCACHED
and enable RWF_UNCACHED. If RWF_UNCACHED is attempted without the file
system supporting it, it'll get errored with -EOPNOTSUPP.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
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 3559446279c1..45510d0b8de0 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -320,6 +320,7 @@ 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_UNCACHED (__force int) RWF_UNCACHED

/* non-RWF related bits - start at 16 */
#define IOCB_EVENTFD (1 << 16)
@@ -354,7 +355,8 @@ struct readahead_control;
{ IOCB_SYNC, "SYNC" }, \
{ IOCB_NOWAIT, "NOWAIT" }, \
{ IOCB_APPEND, "APPEND" }, \
- { IOCB_ATOMIC, "ATOMIC"}, \
+ { IOCB_ATOMIC, "ATOMIC" }, \
+ { IOCB_UNCACHED, "UNCACHED" }, \
{ IOCB_EVENTFD, "EVENTFD"}, \
{ IOCB_DIRECT, "DIRECT" }, \
{ IOCB_WRITE, "WRITE" }, \
@@ -2116,6 +2118,8 @@ struct file_operations {
#define FOP_HUGE_PAGES ((__force fop_flags_t)(1 << 4))
/* Treat loff_t as unsigned (e.g., /dev/mem) */
#define FOP_UNSIGNED_OFFSET ((__force fop_flags_t)(1 << 5))
+/* File system supports uncached read/write buffered IO */
+#define FOP_UNCACHED ((__force fop_flags_t)(1 << 6))

/* Wrap a directory iterator that needs exclusive inode access */
int wrap_directory_iterator(struct file *, struct dir_context *,
@@ -3532,6 +3536,14 @@ 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_UNCACHED) {
+ /* file system must support it */
+ if (!(ki->ki_filp->f_op->fop_flags & FOP_UNCACHED))
+ 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..dc77cd8ae1a3 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_UNCACHED ((__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_UNCACHED)

#define PROCFS_IOCTL_MAGIC 'f'

--
2.45.2