> On 23 Jul 2019, at 10:57 PM, David Sterba <dsterba@xxxxxxx> wrote:
>
> On Wed, Jun 26, 2019 at 04:34:01PM +0800, Anand Jain wrote:
>> Function call chain __btrfs_map_block()->find_live_mirror() uses
>> thread %pid to determine the %mirror_num for the read when mirror_num=0
>> in the argument.
>>
>> This patch introduces a framework so that readmirror is a configurable
>> parameter, with default set to pid.
>>
>> Signed-off-by: Anand Jain <anand.jain@xxxxxxxxxx>
>> ---
>> fs/btrfs/props.c | 41 +++++++++++++++++++++++++++++++++++++++++
>> fs/btrfs/volumes.c | 9 ++++++++-
>> fs/btrfs/volumes.h | 6 ++++++
>> 3 files changed, 55 insertions(+), 1 deletion(-)
>>
>> diff --git a/fs/btrfs/props.c b/fs/btrfs/props.c
>> index f9143f7c006d..0dc26a154a98 100644
>> --- a/fs/btrfs/props.c
>> +++ b/fs/btrfs/props.c
>> @@ -10,6 +10,7 @@
>> #include "ctree.h"
>> #include "xattr.h"
>> #include "compression.h"
>> +#include "volumes.h"
>>
>> #define BTRFS_PROP_HANDLERS_HT_BITS 8
>> static DEFINE_HASHTABLE(prop_handlers_ht, BTRFS_PROP_HANDLERS_HT_BITS);
>> @@ -312,6 +313,39 @@ static const char *prop_compression_extract(struct inode *inode)
>> return NULL;
>> }
>>
>> +static int prop_readmirror_validate(struct inode *inode, const char *value,
>> + size_t len)
>> +{
>> + struct btrfs_root *root = BTRFS_I(inode)->root;
>> +
>> + if (root->root_key.objectid != BTRFS_FS_TREE_OBJECTID)
>> + return -EINVAL;
>> +
>> + if (!len)
>> + return 0;
>> +
>> + return -EINVAL;
>> +}
>> +
>> +static int prop_readmirror_apply(struct inode *inode, const char *value,
>> + size_t len)
>> +{
>> + struct btrfs_fs_devices *fs_devices = btrfs_sb(inode->i_sb)->fs_devices;
>> +
>> + fs_devices->readmirror_policy = BTRFS_READMIRROR_DEFAULT;
>> +
>> + return 0;
>> +}
>> +
>> +static const char *prop_readmirror_extract(struct inode *inode)
>> +{
>> + /*
>> + * readmirror policy is applied for the whole FS, inheritance is not
>> + * applicable.
>> + */
>
> Extract is the 'get' implementation of the property, not inheritance, or
> I don't understand what does the comment refer to.
prop_handler::extract() is only used by inherit_props(). Readmirror property is for the volume/fsid so prop_handler::inheritable is set to 0. So inherit_props() doesn’t call extract() for readmirror.
The getxattr still work using the xattr interface and will have to mount the root which is I think is ok which is similar to the admin only operations, otherwise we have to introduce a new ioctl.
Thanks, Anand
>> + return NULL;
>
> The return value should reflect the status of the property, ie.
> basically the same value that would set the current state.
>
>> +}
>> +
>> static struct prop_handler prop_handlers[] = {
>> {
>> .xattr_name = XATTR_BTRFS_PREFIX "compression",
>> @@ -320,6 +354,13 @@ static struct prop_handler prop_handlers[] = {
>> .extract = prop_compression_extract,
>> .inheritable = 1
>> },
>> + {
>> + .xattr_name = XATTR_BTRFS_PREFIX "readmirror",
>> + .validate = prop_readmirror_validate,
>> + .apply = prop_readmirror_apply,
>> + .extract = prop_readmirror_extract,
>> + .inheritable = 0
>> + },
>> };
>>
>> static int inherit_props(struct btrfs_trans_handle *trans,
>> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
>> index a13ddba1ebc3..d72850ed4f88 100644
>> --- a/fs/btrfs/volumes.c
>> +++ b/fs/btrfs/volumes.c
>> @@ -5490,7 +5490,14 @@ static int find_live_mirror(struct btrfs_fs_info *fs_info,
>> else
>> num_stripes = map->num_stripes;
>>
>> - preferred_mirror = first + current->pid % num_stripes;
>> + switch(fs_info->fs_devices->readmirror_policy) {
>> + case BTRFS_READMIRROR_DEFAULT:
>> + /* fall through */
>> + default:
>> + /* readmirror as per thread pid */
>> + preferred_mirror = first + current->pid % num_stripes;
>> + break;
>> + }
>>
>> if (dev_replace_is_ongoing &&
>> fs_info->dev_replace.cont_reading_from_srcdev_mode ==
>> diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
>> index 7f6aa1816409..e985d2133c0a 100644
>> --- a/fs/btrfs/volumes.h
>> +++ b/fs/btrfs/volumes.h
>> @@ -219,6 +219,10 @@ BTRFS_DEVICE_GETSET_FUNCS(total_bytes);
>> BTRFS_DEVICE_GETSET_FUNCS(disk_total_bytes);
>> BTRFS_DEVICE_GETSET_FUNCS(bytes_used);
>>
>> +enum btrfs_readmirror_policy {
>> + BTRFS_READMIRROR_DEFAULT,
>> +};
>> +
>> struct btrfs_fs_devices {
>> u8 fsid[BTRFS_FSID_SIZE]; /* FS specific uuid */
>> u8 metadata_uuid[BTRFS_FSID_SIZE];
>> @@ -269,6 +273,8 @@ struct btrfs_fs_devices {
>> struct kobject fsid_kobj;
>> struct kobject *device_dir_kobj;
>> struct completion kobj_unregister;
>> +
>> + int readmirror_policy;
>> };
>>
>> #define BTRFS_BIO_INLINE_CSUM_SIZE 64
>> --
>> 2.20.1 (Apple Git-117)
