Feature #19819
closed
Add support of FS_IOC_FIEMAP ioctl on files, accessible through CephFS
Added by Марк Коренберг about 7 years ago.
Updated almost 7 years ago.
Category:
Administration/Usability
Description
The purpose of this -- is to have standard interface for examining allocated extents of the files. For example, xfs_io command can use this to show extents on many filesystems, but unfortunatelly, not on CephFS.
(Also, can anyone tell which command from ceph toolbox should I use to show really allocated segents of the file)
- Project changed from Ceph to CephFS
- Category set to Administration/Usability
This is pretty infeasible right now -- nothing tracks which bits of a file are allocated or exist. The closest it comes is max size and the ability in RADOS to query specific allocations.
Марк: is this ticket describing something you want to work on, or is it just a request? In either case, what's the motivation?
This is feature request. I have no skills and proper knowledge on CephFS to implement this feature.
Motivation -- is ability to view which parts of file has been actually allocated, i.e. to know how many space is used actually for specific file.
Now, files on CephFS, create using `truncate` and `fallocate` are indistinguishable, and both are created momentarily. Moreover, fallocate on CephFS is a fake. It doesn't allocate space actually.
- Status changed from New to Rejected
Okay. I'm going to close this, because implementing that ioctl efficiently isn't doable without major changes to how CephFS stores files (i.e. making CephFS keep an index of which parts of a file have been written).
If you have an application that needs a record of which parts of a file it has written, I would suggest implementing that within your application.
Please don't close, since issue is valid, and maybe someone wil eventually fix it.
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