As you can see in the below example, we find a number of bioset processes running on our Oracle Linux machine;
[root@docker ~]# ps -ef|grep bioset root 30 2 0 12:04 ? 00:00:00 [bioset] root 299 2 0 12:04 ? 00:00:00 [bioset] root 302 2 0 12:04 ? 00:00:00 [bioset] root 4136 2 0 14:20 ? 00:00:00 [bioset] root 4138 2 0 14:20 ? 00:00:00 [bioset] root 4140 2 0 14:20 ? 00:00:00 [bioset] root 4379 3470 0 14:35 pts/0 00:00:00 grep bioset [root@docker ~]#
Finding bioset
To find out what bioset is and where it is being spawned from you can look at your processes in a number of ways. You can use the below command which provides a nice tree view of all the processes based upon the ps command or you can use the standard pstree command.
ps axfo pid,euser,egroup,args
using the above command we get the below output (cut down to the relevant part only);
As you can see bioset is a mentioned a number of times, and always as a "child" from kthreadd. Where kthreadd is within Oracle Linux (Linux in general) the kernel thread daemon and by doing so it is one of the backbone components of the Linux kernel which makes sure your kernel threads are handled in the right manner.
root@docker ~]# ps axfo pid,euser,egroup,args
PID EUSER EGROUP COMMAND
2 root root [kthreadd]
3 root root \_ [ksoftirqd/0]
5 root root \_ [kworker/0:0H]
6 root root \_ [kworker/u4:0]
7 root root \_ [rcu_sched]
8 root root \_ [rcu_bh]
9 root root \_ [rcuos/0]
10 root root \_ [rcuob/0]
11 root root \_ [migration/0]
12 root root \_ [watchdog/0]
13 root root \_ [watchdog/1]
14 root root \_ [migration/1]
15 root root \_ [ksoftirqd/1]
16 root root \_ [kworker/1:0]
17 root root \_ [kworker/1:0H]
18 root root \_ [rcuos/1]
19 root root \_ [rcuob/1]
20 root root \_ [khelper]
21 root root \_ [kdevtmpfs]
22 root root \_ [netns]
23 root root \_ [perf]
24 root root \_ [khungtaskd]
25 root root \_ [writeback]
26 root root \_ [ksmd]
27 root root \_ [khugepaged]
28 root root \_ [crypto]
29 root root \_ [kintegrityd]
30 root root \_ [bioset]
31 root root \_ [kblockd]
32 root root \_ [ata_sff]
33 root root \_ [md]
34 root root \_ [kworker/0:1]
36 root root \_ [kswapd0]
37 root root \_ [fsnotify_mark]
49 root root \_ [kthrotld]
50 root root \_ [acpi_thermal_pm]
51 root root \_ [kworker/u4:1]
52 root root \_ [kworker/1:1]
53 root root \_ [kpsmoused]
54 root root \_ [bcache]
55 root root \_ [deferwq]
56 root root \_ [kworker/0:2]
200 root root \_ [scsi_eh_0]
201 root root \_ [scsi_tmf_0]
202 root root \_ [scsi_eh_1]
203 root root \_ [scsi_tmf_1]
233 root root \_ [scsi_eh_2]
234 root root \_ [scsi_tmf_2]
298 root root \_ [kdmflush]
299 root root \_ [bioset]
301 root root \_ [kdmflush]
302 root root \_ [bioset]
368 root root \_ [kworker/0:1H]
369 root root \_ [jbd2/dm-1-8]
370 root root \_ [ext4-rsv-conver]
626 root root \_ [iprt-VBoxWQueue]
627 root root \_ [ttm_swap]
738 root root \_ [jbd2/sda1-8]
739 root root \_ [ext4-rsv-conver]
827 root root \_ [kauditd]
889 root root \_ [ipv6_addrconf]
3744 root root \_ [kworker/1:1H]
4122 root root \_ [loop0]
4123 root root \_ [loop1]
4126 root root \_ [kdmflush]
4133 root root \_ [dm_bufio_cache]
4136 root root \_ [bioset]
4137 root root \_ [kcopyd]
4138 root root \_ [bioset]
4139 root root \_ [dm-thin]
4140 root root \_ [bioset]
However, now we know where bioset is commong from and the parent is the kernel thread daemon we still do not know what bioset is doing.
What is bioset
As we now known bioset is part of the Linux kernel, it is used to Block Input Output instructions. This means it is an integrated part of the inner workings of the kernel when operations to a block device need to be done. bioset finds its origin in the struct bios_set located in bio.h within the Linux kernel code. The bio_set struct is shown below and can also be found in the kernel Github code repository.
/*
* bio_set is used to allow other portions of the IO system to
* allocate their own private memory pools for bio and iovec structures.
* These memory pools in turn all allocate from the bio_slab
* and the bvec_slabs[].
*/
#define BIO_POOL_SIZE 2
struct bio_set {
struct kmem_cache *bio_slab;
unsigned int front_pad;
mempool_t *bio_pool;
mempool_t *bvec_pool;
#if defined(CONFIG_BLK_DEV_INTEGRITY)
mempool_t *bio_integrity_pool;
mempool_t *bvec_integrity_pool;
#endif
/*
* Deadlock avoidance for stacking block drivers: see comments in
* bio_alloc_bioset() for details
*/
spinlock_t rescue_lock;
struct bio_list rescue_list;
struct work_struct rescue_work;
struct workqueue_struct *rescue_workqueue;
};
If you explore the Linux kernel code you will find that within /block/bio.c will be include /linux/bio.h . The Linux block I/O subsystem includes bioset and this is a vital part of how BIOs are handled within the kernel.
Below images shows the Linux storage stack for kernel version 4.0 where you can see the flow of BIOs. BIOs are send from LIO (Linux I/O) or the VFS to the block I/O layer who in return will communicate with the I/O scheduler who will schedule the I/O operation to be send on the actual block device.
In conclusion
A lot of posts are being written that would indicate that bioset would be something that could be removed or would be malicious for the system, as outlined in the above post bioset is however a vital part of the Linux Kernel and an integrated part of the I/O subsystem for handling I/O requests in combination with block devices.
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