> On Jul 21, 2017, at 2:11 PM, Jaegeuk Kim <jaeg...@kernel.org> 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 <jaeg...@kernel.org> > --- > 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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