Re: [PATCH] btrfs-progs: Fix seed device bug for btrfs249

[Qu Wenruo <quwenruo.btrfs@gmx.com>]

On 2022/8/11 14:07, hmsjwzb wrote:
> Hi Qu,
>
> Thanks for you reply. I am working on the tree-search based solution.
> I have got the btrfs_dev_item from the chunk tree.
> But I don't know how to tell whether it is a seed device.

You can check the fsid.

Seed device has a different fsid than the one returned by BTRFS_IOC_FS_INFO.

Thanks,
Qu

> Do you have some solution to tell whether it is a seed device or not?
>
> Thanks,
> Flint
>
> On 8/10/22 03:56, Qu Wenruo wrote:
>> Commit message please.
>>
>> On 2022/8/10 15:33, Flint.Wang wrote:
>>> Signed-off-by: Flint.Wang <hmsjwzb@zoho.com>
>>> ---
>>>    cmds/device.c           |  2 +-
>>>    cmds/filesystem-usage.c | 10 +++++-----
>>>    cmds/filesystem-usage.h |  2 +-
>>>    common/utils.c          |  9 +++++----
>>>    common/utils.h          |  2 +-
>>>    ioctl.h                 |  2 ++
>>>    6 files changed, 15 insertions(+), 12 deletions(-)
>>>
>>> diff --git a/cmds/device.c b/cmds/device.c
>>> index 7d3febff..81559110 100644
>>> --- a/cmds/device.c
>>> +++ b/cmds/device.c
>>> @@ -752,7 +752,7 @@ static int _cmd_device_usage(int fd, const char *path, unsigned unit_mode)
>>>        int devcount = 0;
>>>
>>>        ret = load_chunk_and_device_info(fd, &chunkinfo, &chunkcount, &devinfo,
>>> -            &devcount);
>>> +            &devcount, false);
>>>        if (ret)
>>>            goto out;
>>>
>>> diff --git a/cmds/filesystem-usage.c b/cmds/filesystem-usage.c
>>> index 01729e18..b2ed3212 100644
>>> --- a/cmds/filesystem-usage.c
>>> +++ b/cmds/filesystem-usage.c
>>> @@ -693,7 +693,7 @@ out:
>>>     *  This function loads the device_info structure and put them in an array
>>>     */
>>>    static int load_device_info(int fd, struct device_info **device_info_ptr,
>>> -               int *device_info_count)
>>> +               int *device_info_count, bool noseed)
>>>    {
>>>        int ret, i, ndevs;
>>>        struct btrfs_ioctl_fs_info_args fi_args;
>>> @@ -727,7 +727,7 @@ static int load_device_info(int fd, struct device_info **device_info_ptr,
>>>                goto out;
>>>            }
>>>            memset(&dev_info, 0, sizeof(dev_info));
>>> -        ret = get_device_info(fd, i, &dev_info);
>>> +        ret = get_device_info(fd, i, &dev_info, noseed);
>>>
>>>            if (ret == -ENODEV)
>>>                continue;
>>> @@ -779,7 +779,7 @@ out:
>>>    }
>>>
>>>    int load_chunk_and_device_info(int fd, struct chunk_info **chunkinfo,
>>> -        int *chunkcount, struct device_info **devinfo, int *devcount)
>>> +        int *chunkcount, struct device_info **devinfo, int *devcount, bool noseed)
>>>    {
>>>        int ret;
>>>
>>> @@ -791,7 +791,7 @@ int load_chunk_and_device_info(int fd, struct chunk_info **chunkinfo,
>>>            return ret;
>>>        }
>>>
>>> -    ret = load_device_info(fd, devinfo, devcount);
>>> +    ret = load_device_info(fd, devinfo, devcount, noseed);
>>>        if (ret == -EPERM) {
>>>            warning(
>>>            "cannot get filesystem info from ioctl(FS_INFO), run as root");
>>> @@ -1172,7 +1172,7 @@ static int cmd_filesystem_usage(const struct cmd_struct *cmd,
>>>                printf("\n");
>>>
>>>            ret = load_chunk_and_device_info(fd, &chunkinfo, &chunkcount,
>>> -                &devinfo, &devcount);
>>> +                &devinfo, &devcount, true);
>>>            if (ret)
>>>                goto cleanup;
>>>
>>> diff --git a/cmds/filesystem-usage.h b/cmds/filesystem-usage.h
>>> index cab38462..6fd04172 100644
>>> --- a/cmds/filesystem-usage.h
>>> +++ b/cmds/filesystem-usage.h
>>> @@ -45,7 +45,7 @@ struct chunk_info {
>>>    };
>>>
>>>    int load_chunk_and_device_info(int fd, struct chunk_info **chunkinfo,
>>> -        int *chunkcount, struct device_info **devinfo, int *devcount);
>>> +        int *chunkcount, struct device_info **devinfo, int *devcount, bool noseed);
>>>    void print_device_chunks(struct device_info *devinfo,
>>>            struct chunk_info *chunks_info_ptr,
>>>            int chunks_info_count, unsigned unit_mode);
>>> diff --git a/common/utils.c b/common/utils.c
>>> index 1ed5571f..72d50885 100644
>>> --- a/common/utils.c
>>> +++ b/common/utils.c
>>> @@ -285,14 +285,15 @@ void btrfs_format_csum(u16 csum_type, const u8 *data, char *output)
>>>    }
>>>
>>>    int get_device_info(int fd, u64 devid,
>>> -        struct btrfs_ioctl_dev_info_args *di_args)
>>> +        struct btrfs_ioctl_dev_info_args *di_args, bool noseed)
>>>    {
>>>        int ret;
>>> +    unsigned long req = noseed ? BTRFS_IOC_DEV_INFO_NOSEED : BTRFS_IOC_DEV_INFO;
>>>
>>>        di_args->devid = devid;
>>>        memset(&di_args->uuid, '\0', sizeof(di_args->uuid));
>>>
>>> -    ret = ioctl(fd, BTRFS_IOC_DEV_INFO, di_args);
>>> +    ret = ioctl(fd, req, di_args);
>>>        return ret < 0 ? -errno : 0;
>>>    }
>>>
>>> @@ -498,7 +499,7 @@ int get_fs_info(const char *path, struct btrfs_ioctl_fs_info_args *fi_args,
>>>             * search_chunk_tree_for_fs_info() will lacks the devid 0
>>>             * so manual probe for it here.
>>>             */
>>> -        ret = get_device_info(fd, 0, &tmp);
>>> +        ret = get_device_info(fd, 0, &tmp, false);
>>
>> No, I don't think we should go that complex.
>>
>> The root cause is pretty simple, btrfs_ioctl_fs_info() just return RW
>> devices for its fi_args->num_devices.
>>
>> This is fine for most cases, but for seed devices cases, we can not rely
>> on that.
>>
>>
>> Knowing that, it's much easier to fix in user space, do a tree-search
>> ioctl to grab the device items from chunk tree, then we can easily check
>> the total number of devices (including RW and seed devices).
>>
>> With that info, we even have the FSID of each devices, then we can call
>> btrfs_ioctl_dev_info() to get each device.
>>
>>
>> I'd like to have a better optimization, to skip above chunk tree search,
>> but I don't have a quick idea on how to determine if a fs has seed devices.
>>
>>
>> Another more elegant solution is to make btrfs_ioctl_fs_info_args to
>> include one new member, total_devs, so that we can get rid of all the
>> problems.
>>
>> But for compatibility reasons, above tree-search based solution is still
>> needed as a fallback.
>>
>> Thanks,
>> Qu
>>
>>>            if (!ret) {
>>>                fi_args->num_devices++;
>>>                ndevs++;
>>> @@ -521,7 +522,7 @@ int get_fs_info(const char *path, struct btrfs_ioctl_fs_info_args *fi_args,
>>>            memcpy(di_args, &tmp, sizeof(tmp));
>>>        for (; last_devid <= fi_args->max_id && ndevs < fi_args->num_devices;
>>>             last_devid++) {
>>> -        ret = get_device_info(fd, last_devid, &di_args[ndevs]);
>>> +        ret = get_device_info(fd, last_devid, &di_args[ndevs], false);
>>>            if (ret == -ENODEV)
>>>                continue;
>>>            if (ret)
>>> diff --git a/common/utils.h b/common/utils.h
>>> index ea05fe5b..de4f93ca 100644
>>> --- a/common/utils.h
>>> +++ b/common/utils.h
>>> @@ -68,7 +68,7 @@ int lookup_path_rootid(int fd, u64 *rootid);
>>>    int find_mount_fsroot(const char *subvol, const char *subvolid, char **mount);
>>>    int find_mount_root(const char *path, char **mount_root);
>>>    int get_device_info(int fd, u64 devid,
>>> -        struct btrfs_ioctl_dev_info_args *di_args);
>>> +        struct btrfs_ioctl_dev_info_args *di_args, bool noseed);
>>>    int get_df(int fd, struct btrfs_ioctl_space_args **sargs_ret);
>>>
>>>    const char *subvol_strip_mountpoint(const char *mnt, const char *full_path);
>>> diff --git a/ioctl.h b/ioctl.h
>>> index 368a87b2..e68fe58d 100644
>>> --- a/ioctl.h
>>> +++ b/ioctl.h
>>> @@ -883,6 +883,8 @@ static inline char *btrfs_err_str(enum btrfs_err_code err_code)
>>>                        struct btrfs_ioctl_scrub_args)
>>>    #define BTRFS_IOC_DEV_INFO _IOWR(BTRFS_IOCTL_MAGIC, 30, \
>>>                        struct btrfs_ioctl_dev_info_args)
>>> +#define BTRFS_IOC_DEV_INFO_NOSEED _IOR(BTRFS_IOCTL_MAGIC, 30, \
>>> +                       struct btrfs_ioctl_dev_info_args)
>>>    #define BTRFS_IOC_FS_INFO _IOR(BTRFS_IOCTL_MAGIC, 31, \
>>>                                     struct btrfs_ioctl_fs_info_args)
>>>    #define BTRFS_IOC_BALANCE_V2 _IOWR(BTRFS_IOCTL_MAGIC, 32, \