PROBE::IOBLOCK_TRACE.BOUNCE(3stap)

💖 PROBE::IOBLOCK_TRACE.BOUNCE 💖

okay bestie, gather round, because we're reading a SystemTap Tapset Reference page — that's the 3stap manual, section 3, tapset pages — and this one is filed under IO Scheduler and block IO Taps. It's giving kernel-nerd royalty, no cap. 👑

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✨ NAME ✨

probe::ioblock_trace.bounce — fires whenever a buffer bounce is needed for at least one page of a block IO request.

literally the moment the kernel is like "hm, this buffer needs to bounce" and it happens for even one single page of a block IO request. one page. that's all it takes. 💅

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🌸 SYNOPSIS 🌸

probe ioblock_trace.bounce {}

that's it. no arguments, no nothing. she's lowkey minimalist. 🎀

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🦋 VALUES 🦋

all the little goodies this probe hands you when she fires:

• q — the request queue on which this bio was queued.
• 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.
• bytes_done — number of bytes transferred.
• name — name of the probe point.
• vcnt — bio vector count, which represents the number of array elements (page, offset, length) that make up this I/O request.
• bdev_contains — points to the device object which contains the partition (when the bio structure represents a partition).
• devname — device for which a buffer bounce was needed.
• idx — offset into the bio vector array phys_segments - number of segments in this bio after physical address coalescing is performed.
• sector — beginning sector for the entire bio.
• rw — binary trace for read/write request.
• 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
• bdev — target block device.
• opf — operations and flags.

ok the flags bit is a whole mood board of bio states — memorise those numbers, bestie, they're doing numbers. 🔥

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💜 CONTEXT 💜

The process creating a block IO request.

(yes, that's the whole thing. she's concise. main character energy.) ✨

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🌈 SEE ALSO 🌈

• tapset::ioblock(3stap)

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and that's the whole page, periodt. this was SystemTap Tapset Reference, Version, September 2026 — so like, mark your calendar, it's a whole era. 🫶💖🌸