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SubjectRe: [Ocfs2-devel] [PATCH 1/3] ocfs2: add ocfs2_try_rw_lock and ocfs2_try_inode_lock
Hello Changwei,


>>>
> Hi Gang,
>
> On 2017/11/27 17:48, Gang He wrote:
>> Add ocfs2_try_rw_lock and ocfs2_try_inode_lock functions, which
>> will be used in non-block IO scenarios.
>>
>> Signed-off-by: Gang He <ghe@suse.com>
>> ---
>> fs/ocfs2/dlmglue.c | 22 ++++++++++++++++++++++
>> fs/ocfs2/dlmglue.h | 4 ++++
>> 2 files changed, 26 insertions(+)
>>
>> diff --git a/fs/ocfs2/dlmglue.c b/fs/ocfs2/dlmglue.c
>> index 4689940..5cfbd04 100644
>> --- a/fs/ocfs2/dlmglue.c
>> +++ b/fs/ocfs2/dlmglue.c
>> @@ -1742,6 +1742,28 @@ int ocfs2_rw_lock(struct inode *inode, int write)
>> return status;
>> }
>>
>> +int ocfs2_try_rw_lock(struct inode *inode, int write)
>> +{
>> + int status, level;
>> + struct ocfs2_lock_res *lockres;
>> + struct ocfs2_super *osb = OCFS2_SB(inode->i_sb);
>> +
>> + mlog(0, "inode %llu try to take %s RW lock\n",
>> + (unsigned long long)OCFS2_I(inode)->ip_blkno,
>> + write ? "EXMODE" : "PRMODE");
>> +
>> + if (ocfs2_mount_local(osb))
>> + return 0;
>> +
>> + lockres = &OCFS2_I(inode)->ip_rw_lockres;
>> +
>> + level = write ? DLM_LOCK_EX : DLM_LOCK_PR;
>> +
>> + status = ocfs2_cluster_lock(OCFS2_SB(inode->i_sb), lockres, level,
>> + DLM_LKF_NOQUEUE, 0);
>> + return status;
>> +}
>
> The newly added function ocfs2_try_rw_lock almost has the same logic
> with ocfs2_rw_lock.Is it possible to combine them into an unique one?
> That will be more elegant.
I prefer to keep ocfs2_try_rw_lock() separately, since there has been the similar function/code here (e.g. ocfs2_try_open_lock).
second, adding a new ocfs2_try_rw_lock() function can avoid impact the existing code.

>
> Moreover, can you elaborate further why we need a *NOQUEUE* lock for
> supporting non-block aio?
Non-block IO means that the invoking should return with -EAGAIN instead of being blocked to wait for certain resource (e.g. lock, block allocation, etc.).

>
> Why can't we wait for a while to grant a lock request? Is this necessary?
Non-block IO is a way for the upper application to submit IO, if the invoking will be blocked, the invoking will failed with -EAGAIN,
then, the upper application will submit this IO with the normal (block mode) way in a delayed thread, this IO mode will benefit some database application.

>
> Thanks,
> Changwei
>
>> +
>> void ocfs2_rw_unlock(struct inode *inode, int write)
>> {
>> int level = write ? DLM_LOCK_EX : DLM_LOCK_PR;
>> diff --git a/fs/ocfs2/dlmglue.h b/fs/ocfs2/dlmglue.h
>> index a7fc18b..05910fc 100644
>> --- a/fs/ocfs2/dlmglue.h
>> +++ b/fs/ocfs2/dlmglue.h
>> @@ -116,6 +116,7 @@ void ocfs2_refcount_lock_res_init(struct ocfs2_lock_res
> *lockres,
>> int ocfs2_create_new_inode_locks(struct inode *inode);
>> int ocfs2_drop_inode_locks(struct inode *inode);
>> int ocfs2_rw_lock(struct inode *inode, int write);
>> +int ocfs2_try_rw_lock(struct inode *inode, int write);
>> void ocfs2_rw_unlock(struct inode *inode, int write);
>> int ocfs2_open_lock(struct inode *inode);
>> int ocfs2_try_open_lock(struct inode *inode, int write);
>> @@ -140,6 +141,9 @@ int ocfs2_inode_lock_with_page(struct inode *inode,
>> /* 99% of the time we don't want to supply any additional flags --
>> * those are for very specific cases only. */
>> #define ocfs2_inode_lock(i, b, e) ocfs2_inode_lock_full_nested(i, b, e, 0,
> OI_LS_NORMAL)
>> +#define ocfs2_try_inode_lock(i, b, e)\
>> + ocfs2_inode_lock_full_nested(i, b, e, OCFS2_META_LOCK_NOQUEUE,\
>> + OI_LS_NORMAL)
>> void ocfs2_inode_unlock(struct inode *inode,
>> int ex);
>> int ocfs2_super_lock(struct ocfs2_super *osb,
>>

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