blkid_get_cache seems to leak memory

Question

I am doing some linux programming and I encountered a situation where a library function from the blkid library leaks some memory... There is not too much documentation about it (https://www.kernel.org/pub/linux/utils/util-linux/v2.21/libblkid-docs/libblkid-Cache.html) so I turn to the community to find some cure to this problem.

The function is blkid_get_cache and valgrind reports:

==29769== 4,129 (72 direct, 4,057 indirect) bytes in 1 blocks are definitely lost in loss record 68 of 69
==29769==    at 0x4C29DB4: calloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==29769==    by 0x67360BB: blkid_get_cache (in /lib/x86_64-linux-gnu/libblkid.so.1.1.0)
==29769==    by 0x652DBAC: gather_disk_stat() (disk_status.cpp:96)
==29769==    by 0x652DD5A: execute (disk_status.cpp:124)
==29769==    by 0x42599B: PluginHelper::executeClientPlugin(plugin_descriptor*) (plugin_helper.cpp:333)
==29769==    by 0x432BB5: main (main.cpp:48)

Now, this piece of code will be used in a daemon process which is supposed to run 24/7 so I would like to avoid the uncontrollable growth of memory.

Did anyone work with libblkid til now? How to fix this memory issue? (At an extreme case I could just free() it ... but would it affect system stability?)

Answer 1

Are you using blkid_put_cache()?

For the README of libblkid:

If you have called blkid_get_cache(), you should call blkid_put_cache() when you are done using the blkid library functions. This will save the cache to the blkid.tab file, if you have write access to the file. It will also free all associated devices and tags:

blkid_put_cache(cache);