On Tue, Feb 28, 2017 at 06:57:30AM -0800, Christoph Hellwig wrote:
> This fcntl can be used to query I/O parameters for the given file
> descriptor. Initially it is used for the I/O alignment and atomic
> write parameters.
>
> Signed-off-by: Christoph Hellwig <hch@xxxxxx>
> ---
> fs/fcntl.c | 18 ++++++++++++++++++
> include/linux/fs.h | 1 +
> include/uapi/linux/fcntl.h | 16 ++++++++++++++++
> 3 files changed, 35 insertions(+)
>
> diff --git a/fs/fcntl.c b/fs/fcntl.c
> index ca5d228be7ea..248fb4cc66a6 100644
> --- a/fs/fcntl.c
> +++ b/fs/fcntl.c
> @@ -241,6 +241,21 @@ static int f_getowner_uids(struct file *filp, unsigned long arg)
> }
> #endif
>
> +static int fcntl_ioinfo(struct file *file, void __user *argp)
> +{
> + struct fcntl_ioinfo fio = { 0, };
> +
> + if (file->f_op->ioinfo) {
> + int ret = file->f_op->ioinfo(file, &fio);
> + if (ret)
> + return ret;
> + }
> +
> + if (copy_to_user(argp, &fio, sizeof(fio)))
> + return -EFAULT;
> + return 0;
> +}
> +
> static long do_fcntl(int fd, unsigned int cmd, unsigned long arg,
> struct file *filp)
> {
> @@ -335,6 +350,9 @@ static long do_fcntl(int fd, unsigned int cmd, unsigned long arg,
> case F_GET_SEALS:
> err = shmem_fcntl(filp, cmd, arg);
> break;
> + case F_IOINFO:
> + err = fcntl_ioinfo(filp, (void __user *)arg);
> + break;
> default:
> break;
> }
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 2ba074328894..33b08a8c2bc3 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -1680,6 +1680,7 @@ struct file_operations {
> u64);
> ssize_t (*dedupe_file_range)(struct file *, u64, u64, struct file *,
> u64);
> + int (*ioinfo)(struct file *, struct fcntl_ioinfo *);
> };
>
> struct inode_operations {
> diff --git a/include/uapi/linux/fcntl.h b/include/uapi/linux/fcntl.h
> index beed138bd359..6b0aaba7c623 100644
> --- a/include/uapi/linux/fcntl.h
> +++ b/include/uapi/linux/fcntl.h
> @@ -42,6 +42,22 @@
> #define F_SEAL_WRITE 0x0008 /* prevent writes */
> /* (1U << 31) is reserved for signed error codes */
>
> +
> +#define F_IOINFO (F_LINUX_SPECIFIC_BASE + 11)
> +
> +struct fcntl_ioinfo {
> + __u16 fio_flags; /* FIO_FL_* */
> + __u16 fio_alignment; /* required I/O alignment on disk */
Hm... is fio_alignment is specified in units of bytes? If so, then
shouldn't this be a __u32 so that we can handle some weird future device
that wants, say, 1MB alignment for its atomic IO?
I'm not sure there /are/ such weird devices, and the current patchset
assumes (probably sanely) that atomic requests only have to be
lba-aligned, but otoh this is a userland field and we have plenty of
reserved space.
Though, now that I look at the XFS ioinfo patch, I guess fio_alignment
is set only for O_DIRECT files? So it's really the required alignment
for directio operations.
(Now I think I'm simply confused about this field.)
--D
> + __u32 __reserved1; /* must be zero */
> + __u64 fio_max_atomic; /* max size for atomic writes */
> + __u64 __reserved2[14];/* must be zero */
> +};
> +
> +/* supports atomic writes using O_(D)SYNC */
> +#define FIO_FL_ATOMIC_OSYNC (1 << 0)
> +/* supports atomic writes committed using fsync/fdatasync/msync */
> +#define FIO_FL_ATOMIC_FSYNC (1 << 1)
> +
> /*
> * Types of directory notifications that may be requested.
> */
> --
> 2.11.0
>
> --
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