OpenAFS client does not flush pages for new empty files

[Chris J Arges]

[ Impact ]

This affects all versions with Linux kernel commit a32ea1e1f925399e0d81ca3f7394a44a6dafa12c. This includes v2.6.23 to the most recent kernel.

This affects precise and quantal versions.

An upstream fix for 1.6.x clients is here:
http://git.openafs.org/?p=openafs.git;a=patch;h=ad4e634051e18fa5bd07016b6405e53e236c2f45

Essentially this patch ensures we flush pages for empty files.

[ Test Case ]

Consider two OpenAFS clients: client A and client B. Client B is running Linux kernel v2.6.23 or higher, and client A is running on any platform:

 1. Client A creates a new file
 2. Client B reads the new, empty file
 3. Client A writes data to the new file
 4. Client B reads the new, now non-empty file again

Client B will now read 4096 of NUL bytes, followed by the actual file data. If an application is copying file data out of AFS, or to another location in AFS, this error will become permanent, since the NUL bytes are stored in a new file.

Note that this issue only occurs for files that have never contained any data. In the above example, if client A had truncated an existing non-empty file to 0 bytes instead of creating a new empty file, the issue would not occur.

The most common occurrence of this issue tends to be when client A is copying a large file into AFS, and client B is trying to read the file as it is being copied. Client A will create the empty file as soon as it starts copying, but the file contents will not be written to the fileserver until later.

[ Regression Potential ]

This is an upstream patch, and this code is present in versions in Raring and beyond.
A test build has been used to verify this fix already.

[Chris J Arges (arges)]

uploaded for P/Q

[Brian Murray (brian-murray)]

Hello Chris, or anyone else affected,

Accepted openafs into precise-proposed. The package will build now and be available at http://launchpad.net/ubuntu/+source/openafs/1.6.1-1+ubuntu0.3 in a few hours, and then in the -proposed repository.

Please help us by testing this new package. See https://wiki.ubuntu.com/Testing/EnableProposed for documentation how to enable and use -proposed. Your feedback will aid us getting this update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug, mentioning the version of the package you tested, and change the tag from verification-needed to verification-done. If it does not fix the bug for you, please add a comment stating that, and change the tag to verification-failed. In either case, details of your testing will help us make a better decision.

Further information regarding the verification process can be found at https://wiki.ubuntu.com/QATeam/PerformingSRUVerification . Thank you in advance!

[Brian Murray (brian-murray)]

Hello Chris, or anyone else affected,

Accepted openafs into quantal-proposed. The package will build now and be available at http://launchpad.net/ubuntu/+source/openafs/1.6.1-2+ubuntu2.2 in a few hours, and then in the -proposed repository.

Please help us by testing this new package. See https://wiki.ubuntu.com/Testing/EnableProposed for documentation how to enable and use -proposed. Your feedback will aid us getting this update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug, mentioning the version of the package you tested, and change the tag from verification-needed to verification-done. If it does not fix the bug for you, please add a comment stating that, and change the tag to verification-failed. In either case, details of your testing will help us make a better decision.

Further information regarding the verification process can be found at https://wiki.ubuntu.com/QATeam/PerformingSRUVerification . Thank you in advance!

[Chris J Arges (arges)]

Verified in P/Q.

[Launchpad Janitor (janitor)]

This bug was fixed in the package openafs - 1.6.1-2+ubuntu2.2

---------------
openafs (1.6.1-2+ubuntu2.2) quantal; urgency=low

  * 0013-afs-Do-not-skip-flushing-pages-for-dv-0-files.patch:
    Fix files with NUL in first 4096 bytes (LP: #1263158)
 -- Chris J Arges <email address hidden> Fri, 20 Dec 2013 10:58:10 -0600

[Scott Kitterman (kitterman)]

The verification of the Stable Release Update for openafs has completed successfully and the package has now been released to -updates. Subsequently, the Ubuntu Stable Release Updates Team is being unsubscribed and will not receive messages about this bug report. In the event that you encounter a regression using the package from -updates please report a new bug using ubuntu-bug and tag the bug report regression-update so we can easily find any regresssions.

[Launchpad Janitor (janitor)]

This bug was fixed in the package openafs - 1.6.1-1+ubuntu0.3

---------------
openafs (1.6.1-1+ubuntu0.3) precise; urgency=low

  * 0013-afs-Do-not-skip-flushing-pages-for-dv-0-files.patch:
    Fix files with NUL in first 4096 bytes (LP: #1263158)
 -- Chris J Arges <email address hidden> Thu, 19 Dec 2013 17:57:47 -0600