> On Jul 21, 2017, at 2:11 PM, Jaegeuk Kim <jaegeuk@xxxxxxxxxx> wrote:
>
> This patch adds an ioctl to provide feature information to user.
> For exapmle, SQLite can use this ioctl to detect whether f2fs support atomic
> write or not.
Just for reference, ext4 exposes functionality that the kernel supports via
a file in /sys/fs/ext4/features/{feature_name} so that it is possible to
check [ -e /sys/fs/ext4/features/lazy_itable_init ] in a shell script also.
There are also per-filesystem tunables in /sys/fs/ext4/{device}/ and it
wouldn't be a bad idea to expose per-filesystem features something like
/sys/fs/{fstype}/{device}/features/{feature_name} so that it is easily
checked by userspace tools using [ -e $feature ] in bash or access()
in programs rather than an ioctl.
Cheers, Andreas
>
> Signed-off-by: Jaegeuk Kim <jaegeuk@xxxxxxxxxx>
> ---
> fs/f2fs/f2fs.h | 2 ++
> fs/f2fs/file.c | 13 +++++++++++++
> 2 files changed, 15 insertions(+)
>
> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> index e06d4e4b4579..5c46a462b56e 100644
> --- a/fs/f2fs/f2fs.h
> +++ b/fs/f2fs/f2fs.h
> @@ -112,6 +112,7 @@ struct f2fs_mount_info {
>
> #define F2FS_FEATURE_ENCRYPT 0x0001
> #define F2FS_FEATURE_BLKZONED 0x0002
> +#define F2FS_FEATURE_ATOMIC_WRITE 0x0004
>
> #define F2FS_HAS_FEATURE(sb, mask) \
> ((F2FS_SB(sb)->raw_super->feature & cpu_to_le32(mask)) != 0)
> @@ -308,6 +309,7 @@ static inline bool __has_cursum_space(struct f2fs_journal *journal,
> struct f2fs_flush_device)
> #define F2FS_IOC_GARBAGE_COLLECT_RANGE _IOW(F2FS_IOCTL_MAGIC, 11, \
> struct f2fs_gc_range)
> +#define F2FS_IOC_GET_FEATURES _IOR(F2FS_IOCTL_MAGIC, 12, __u32)
>
> #define F2FS_IOC_SET_ENCRYPTION_POLICY FS_IOC_SET_ENCRYPTION_POLICY
> #define F2FS_IOC_GET_ENCRYPTION_POLICY FS_IOC_GET_ENCRYPTION_POLICY
> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
> index 2706130c261b..0e07b5b18cfa 100644
> --- a/fs/f2fs/file.c
> +++ b/fs/f2fs/file.c
> @@ -2384,6 +2384,16 @@ static int f2fs_ioc_flush_device(struct file *filp, unsigned long arg)
> return ret;
> }
>
> +static int f2fs_ioc_get_features(struct file *filp, unsigned long arg)
> +{
> + struct inode *inode = file_inode(filp);
> + u32 sb_feature = le32_to_cpu(F2FS_I_SB(inode)->raw_super->feature);
> +
> + /* Must validate to set it with SQLite behavior in Android. */
> + sb_feature |= F2FS_FEATURE_ATOMIC_WRITE;
> +
> + return put_user(sb_feature, (u32 __user *)arg);
> +}
>
> long f2fs_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
> {
> @@ -2426,6 +2436,8 @@ long f2fs_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
> return f2fs_ioc_move_range(filp, arg);
> case F2FS_IOC_FLUSH_DEVICE:
> return f2fs_ioc_flush_device(filp, arg);
> + case F2FS_IOC_GET_FEATURES:
> + return f2fs_ioc_get_features(filp, arg);
> default:
> return -ENOTTY;
> }
> @@ -2491,6 +2503,7 @@ long f2fs_compat_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
> case F2FS_IOC_DEFRAGMENT:
> case F2FS_IOC_MOVE_RANGE:
> case F2FS_IOC_FLUSH_DEVICE:
> + case F2FS_IOC_GET_FEATURES:
> break;
> default:
> return -ENOIOCTLCMD;
> --
> 2.13.0.rc1.294.g07d810a77f-goog
>
Cheers, Andreas
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