[LU-2441] Temporary file support

• Type: Improvement
• Resolution: Fixed
• Priority: Minor
• Fix Version/s: Lustre 2.4.0
• Affects Version/s: Lustre 2.4.0
• Assignee: Jodi Levi (Inactive)
• Reporter: Johann Lombardi (Inactive)

Description

Having a generic mechanism to create temporary files (~ open/unlinked files) would be useful not only for HSM (restore is done in a separate file), but also for some applications which may want to create such a file w/o modifying the time attributes of the parent directory.

A temporary file has the following properties:

• it inherits the striping configuration of the parent directory
• it does not change the time attributes of the parent directory
• no direntry is inserted in the parent directory
• the file is directly linked to PENDING and is thus considered as a open-unlinked file
• if the file needs to be opened multiple times (in addition to the creator), this should be done via open_by_fid.

A temporary file could be created via a regular open/creat call with a special - maybe binary - name to prevent conflict with legacy files. For DNE support, there is a requirement to be able to specify in the filename the MDT index where to create the file.

Assigning the bug to Jodi since i can't assign it to Jacques-Charles.

Issue Links

• is related to: LU-4021 Volatile files should be accessible on all clients
• is related to: LU-9512 Implement O_TMPFILE for Lustre
• is related to: LU-12516 volatile file creation in .lustre/fid/

Comments

[Jodi Levi (Inactive)]

With Change,4836 landed can this ticket be closed?

[jacques-charles lafoucriere]

Patch at http://review.whamcloud.com/4836
Non insertion of direntry in parent directory is missing in this first patch (will be done soon)

[Andreas Dilger]

We need to have an llapi_file_open_unlinked() (or some similarly named) function (similar to llapi_file_open_pool()) to use for tools needing this ability. If we don't think that the Lustre code for creating open-unlinked files can be added in time for 2.4, then at least the llapi_file_open_unlinked() function could start by calling llapi_file_open_pool() to create a regular file using mkstemp() and then immediately unlink() the filename it before returning the file descriptor to the caller.

LU-2182 also has some discussion about having an improved API for passing the layout to/from userspace, and ideally we would use the new API for this new function.