On Tue, Apr 3, 2012 at 6:20 AM, Xavier Hernandez <xhernandez@xxxxxxxxxx> wrote:
Hello developers,
I'm currently trying to implement a new method for managing inode and entry modifications that will be faster (I hope) than the current method for the most common cases. To do so I need to know exactly how the locking mechanism works. I have been browsing the source code and doing some tests, and I would like to be sure that I have understood it correctly before continuing.
All information is based on latest qa releases from 3.3 branch.
My understanding is this:
- There are three locking fops: lk, inodelk and entrylk.
- Client application locks created using fcntl() are received by the translators as lk requests.
- All other functionalities of lk fop are not currently used by any translator (I mean F_RESLK_LCK, F_RESLK_LCKW, F_RESLK_UNLCK and F_GETLK_FD).
- inodelk and entrlylk are only used by AFR to lock inodes or directory entries before modification.
- Translators don't generate lk requests internally.
- Client application requests cannot directly generate an inodelk or entrylk requests.
Correct so far.
- inodelk and entrylk locks are always mandatory.
inodelk and entrylk are always advisory. Never mandatory (at least so far)
- lk locks may be mandatory or advisory.
mandatory mode is not tested for a very long time.
- lk and inodelk are independent from each other, meaning that a lock using lk will not be visible to inodelk and will not block it. inodelk won't block lk requests neither.
- User requests can only be blocked by lk created locks
Correct, and only if mandatory locks are enabled (which isn't tested right now)
(if a write request from user is allowed to pass without using inodelk, it won't be blocked by a previous inodelk).
inodelks are never mandatory, so the question does not apply
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