[prev in list] [next in list] [prev in thread] [next in thread]
List: linux-btrfs
Subject: Re: [PATCH 1/5] btrfs: Make async snapshot ioctl more generic
From: Li Zefan <lizf () cn ! fujitsu ! com>
Date: 2010-11-30 1:13:18
Message-ID: 4CF44FAE.1010603 () cn ! fujitsu ! com
[Download RAW message or body]
Goffredo Baroncelli wrote:
> Hi Li,
>
> great work, but I have some suggestions:
>
> On Monday, 29 November, 2010, Li Zefan wrote:
>> So we don't have to add new structures as we create more ioctls
>> for snapshots.
>>
>> Now to create async snapshot, set BTRFS_SNAPSHOT_CREATE_ASYNC bit of
>> vol_arg_v2->flags, and then call ioctl(BTRFS_IOCT_SNAP_CREATE_V2).
>>
>> Note: this changes the async snapshot ioctl ABI, which was merged
>> in .37 merge window, so we have to make this change into .37.
>>
>> Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
>> ---
>> fs/btrfs/ioctl.c | 34 +++++++++++++++++++++-------------
>> fs/btrfs/ioctl.h | 12 ++++++++----
>> 2 files changed, 29 insertions(+), 17 deletions(-)
>>
>> diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
>> index 463d91b..d3f1a60 100644
>> --- a/fs/btrfs/ioctl.c
>> +++ b/fs/btrfs/ioctl.c
>> @@ -935,23 +935,31 @@ out:
>>
>> static noinline int btrfs_ioctl_snap_create(struct file *file,
>> void __user *arg, int subvol,
>> - int async)
>> + bool v2)
>
> This is a aesthetic suggestion: instead of passing a flag called v2 I suggest
> to add two wrapper functions, which extract the parameters and passes all
> available parameter to the "generic" function. Something like:
>
Sure, as long as it won't result in code duplication and can
improve readability.
> static inline btrfs_ioctl_snap_create_v1(struct file *file,
> void __user *arg, int subvol)
> {
> vol_args = memdup_user(arg, sizeof(*vol_args));
> if (IS_ERR(vol_args))
> return PTR_ERR(vol_args);
> name = vol_args->name;
> fd = vol_args->fd;
> vol_args->name[BTRFS_PATH_NAME_MAX] = '\0';
>
> btrfs_ioctl_snap_create_generic(file, subvol, name, fd, 0, 0);
>
> }
>
> static inline btrfs_ioctl_snap_create_v2(struct file *file,
> void __user *arg, int subvol,
> )
> {
> vol_args_v2 = memdup_user(arg, sizeof(*vol_args_v2));
> if (IS_ERR(vol_args_v2))
> return PTR_ERR(vol_args_v2);
>
> ret = snap_check_flags(vol_args_v2->flags, true);
> if (ret)
> goto out;
>
> name = vol_args_v2->name;
> fd = vol_args_v2->fd;
> vol_args_v2->name[BTRFS_SNAPSHOT_NAME_MAX] = '\0';
> if (vol_args_v2->flags & BTRFS_SNAPSHOT_CREATE_ASYNC)
> async = true;
> if (vol_args_v2->flags & BTRFS_SNAPSHOT_RDONLY)
> readonly = true;
>
> btrfs_ioctl_snap_create_generic(file, subvol, name, fd, async,
> readonly);
>
> }
>
> and
>
> case BTRFS_IOC_SNAP_CREATE:
> return btrfs_ioctl_snap_create_v1(file, argp, 0);
> case BTRFS_IOC_SNAP_CREATE_V2:
> return btrfs_ioctl_snap_create_v2(file, argp, 0);
>
>
> Frankly speaking, we could get rid of the subvol parameter adding another
> wrapper function like "btrfs_ioctl_subvol_create( )", but this would be
> another story :)
>
I thought about that too.
>> {
>> struct btrfs_ioctl_vol_args *vol_args = NULL;
>> - struct btrfs_ioctl_async_vol_args *async_vol_args = NULL;
>> + struct btrfs_ioctl_vol_args_v2 *vol_args_v2 = NULL;
>> char *name;
>> u64 fd;
>> u64 transid = 0;
>> + bool async = false;
>> int ret;
>>
>> - if (async) {
>> - async_vol_args = memdup_user(arg, sizeof(*async_vol_args));
>> - if (IS_ERR(async_vol_args))
>> - return PTR_ERR(async_vol_args);
>> + if (v2) {
>> + vol_args_v2 = memdup_user(arg, sizeof(*vol_args_v2));
>> + if (IS_ERR(vol_args_v2))
>> + return PTR_ERR(vol_args_v2);
>>
>> - name = async_vol_args->name;
>> - fd = async_vol_args->fd;
>> - async_vol_args->name[BTRFS_SNAPSHOT_NAME_MAX] = '\0';
>> + if (vol_args_v2->flags & ~BTRFS_SNAPSHOT_CREATE_ASYNC) {
>> + ret = -EINVAL;
>> + goto out;
>> + }
>> +
>> + name = vol_args_v2->name;
>> + fd = vol_args_v2->fd;
>> + vol_args_v2->name[BTRFS_SNAPSHOT_NAME_MAX] = '\0';
>> + if (vol_args_v2->flags & BTRFS_SNAPSHOT_CREATE_ASYNC)
>> + async = true;
>> } else {
>> vol_args = memdup_user(arg, sizeof(*vol_args));
>> if (IS_ERR(vol_args))
>> @@ -966,13 +974,13 @@ static noinline int btrfs_ioctl_snap_create(struct
> file *file,
>>
>> if (!ret && async) {
>> if (copy_to_user(arg +
>> - offsetof(struct btrfs_ioctl_async_vol_args,
>> + offsetof(struct btrfs_ioctl_vol_args_v2,
>> transid), &transid, sizeof(transid)))
>> return -EFAULT;
>> }
>> -
>> +out:
>> kfree(vol_args);
>> - kfree(async_vol_args);
>> + kfree(vol_args_v2);
>>
>> return ret;
>> }
>> @@ -2235,7 +2243,7 @@ long btrfs_ioctl(struct file *file, unsigned int
>> return btrfs_ioctl_getversion(file, argp);
>> case BTRFS_IOC_SNAP_CREATE:
>> return btrfs_ioctl_snap_create(file, argp, 0, 0);
>> - case BTRFS_IOC_SNAP_CREATE_ASYNC:
>> + case BTRFS_IOC_SNAP_CREATE_V2:
>> return btrfs_ioctl_snap_create(file, argp, 0, 1);
>> case BTRFS_IOC_SUBVOL_CREATE:
>> return btrfs_ioctl_snap_create(file, argp, 1, 0);
>> diff --git a/fs/btrfs/ioctl.h b/fs/btrfs/ioctl.h
>> index 17c99eb..bc70584 100644
>> --- a/fs/btrfs/ioctl.h
>> +++ b/fs/btrfs/ioctl.h
>> @@ -30,10 +30,14 @@ struct btrfs_ioctl_vol_args {
>> char name[BTRFS_PATH_NAME_MAX + 1];
>> };
>>
>> -#define BTRFS_SNAPSHOT_NAME_MAX 4079
>> -struct btrfs_ioctl_async_vol_args {
>> +#define BTRFS_SNAPSHOT_CREATE_ASYNC (1ULL << 0)
>> +
>> +#define BTRFS_SNAPSHOT_NAME_MAX 4039
>> +struct btrfs_ioctl_vol_args_v2 {
>> __s64 fd;
>> __u64 transid;
>> + __u64 flags;
>> + __u64 unused[4];
>> char name[BTRFS_SNAPSHOT_NAME_MAX + 1];
>> };
>
> Why the unused fields ? What happens if you use a more recent btrfs-tools
> which take advantage of these fields but the kernel is an old one ? At the
It's common that we reserve some place in an ABI for future expansion.
If later those unused bytes are used, it should make sure it won't
break old kernels.
> minimum please check the flags so
> (flags^(BTRFS_SNAPSHOT_CREATE_ASYNC|BTRFS_SNAPSHOT_RDONLY)) == 0
This is checked.
> and
> unused[0..3] == 0
No, we don't need to check this. I don't think other ioctls that have
reserved bytes check this.
>
> For future expansion I suggest to use a different ioctl. To me it seems a more
> robust API.
I'd like to avoid new ioctls if possible. If we had had some reserved
bytes in struct btrfs_ioctl_vol_args, we wouldn't need to create
a v2 ioctl.
>
>>
>> @@ -187,6 +191,6 @@ struct btrfs_ioctl_space_args {
>> struct btrfs_ioctl_space_args)
>> #define BTRFS_IOC_START_SYNC _IOR(BTRFS_IOCTL_MAGIC, 24, __u64)
>> #define BTRFS_IOC_WAIT_SYNC _IOW(BTRFS_IOCTL_MAGIC, 22, __u64)
>> -#define BTRFS_IOC_SNAP_CREATE_ASYNC _IOW(BTRFS_IOCTL_MAGIC, 23, \
>> - struct btrfs_ioctl_async_vol_args)
>> +#define BTRFS_IOC_SNAP_CREATE_V2 _IOW(BTRFS_IOCTL_MAGIC, 23, \
>> + struct btrfs_ioctl_vol_args_v2)
>
> I repeat: great work, please take my comments only a suggestion to improve
> instead of an empty criticism.
>
Thanks!
> Regards
> G.Baroncelli
>
>> #endif
>> --
>> 1.6.3
>>
--
To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
[prev in list] [next in list] [prev in thread] [next in thread]
Configure |
About |
News |
Add a list |
Sponsored by KoreLogic