PROBE::IOBLOCK.REQ(3stap) IO Scheduler and block IO Taps PROBE::IOBLOCK.REQ(3stap)

# [NAME](#NAME)

probe::ioblock.request - Fires whenever making a generic block I/O request.

# [SYNOPSIS](#SYNOPSIS)

```
probe ioblock.request {}
```

# [VALUES](#VALUES)

*size*

total size in bytes

*p\_start\_sect*

points to the start sector of the partition structure of the device

*ino*

i-node number of the mapped file

*name*

name of the probe point

*vcnt*

bio vector count which represents number of array element (page, offset, length) which make up this I/O request

*bdev\_contains*

points to the device object which contains the partition (when bio structure represents a partition)

*sector*

beginning sector for the entire bio

*idx*

offset into the bio vector array

*devname*

block device name

*flags*

see below BIO\_UPTODATE 0 ok after I/O completion BIO\_RW\_BLOCK 1 RW\_AHEAD set, and read/write would block BIO\_EOF 2 out-out-bounds error BIO\_SEG\_VALID 3 nr\_hw\_seg valid BIO\_CLONED 4 doesn't own data BIO\_BOUNCED 5 bio is a bounce bio BIO\_USER\_MAPPED 6 contains user pages BIO\_EOPNOTSUPP 7 not supported

*rw*

binary trace for read/write request

*phys\_segments*

number of segments in this bio after physical address coalescing is performed

*hw\_segments*

number of segments after physical and DMA remapping hardware coalescing is performed

*bdev*

target block device

*opf*

operations and flags

# [CONTEXT](#CONTEXT)

The process makes block I/O request

# [SEE ALSO0](#SEE_ALSO0)

[*tapset::ioblock*(3stap)](/man/enterprise-packages/systemtap/tapset::ioblock.3stap)

September 2026 SystemTap Tapset Reference Ver

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Document: probe::ioblock.request(3stap) from systemtap 5.6-r0 (Chainguard OS)
Source: https://sourceware.org/git/systemtap.git