Dear all,
I'm an android developer in charge of sqlite database.
Some days ago, I'd got a SIGBUS error from sqlite when there is no space in
current partition and WAL journal mode is used.
This error was occurred from memset function in libc that was called by
libsqlite and debugging information shows shm file was related to this issue.
Following sequence shows how to generate this error.
1) Make disk full
2) Reboot device - wal and shm files are remained in some applications folder
3) Do 1) ~ 2) until free space remained under 32KB
4) SIGBUS error is occurred randomly
I'd tried to solve this problem and guessed following scenario.
1) shm file is truncated to zero size by calling robust_truncate function when
a new connection is opened in unixOpenSharedMemory
2) shm file is extended to 32KB by calling robust_truncate function in
unixShmMap
3) mmap function is called with 32KB length
In my guess, problem is occurred from robust_truncate or mmap functions,
because of they didn't returned error code whether shm file is extended to 32KB
or not on disk full status.
robust_truncate and mmap may caused illegal memset operation because of shm
file actually doesn't have 32KB size, it may less than 32KB.
Interesting point is when I tested it with above scenario, there was a shm file
that has 32KB size.
It is impossible because of there was no space to make 32KB sized file in
current partiton.
Whatever, I'd changed unixOpenSharedMemory to solve it.
1) make a shm file and write null data until 32KB if this file doesn't exists
- return SQLITE_FULL error when write operation is failed
2) write null data until 32KB if this file exists and got write lock instead of
calling truncate function to shrink shm file to zero size
- return same error code when it failed
By changed source, I could solve this problem.
Sqlite returns SQLITE_FULL errors only without SIGBUS core dump.
However, this instant code changing may not be a good solution.
I wish to get better comment or source patches from here.
Thank you for reading this including my poor english. :)
Best wishes,
Jang.
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