FEMU does not receive actions generated by nvme-cli.

[allencho1222]

version info:

• Guest OS: Ubuntu 22.04 (kernel version: 5.19.17-051917-generic)
  • Kernel is not modified as shown in here.
• FEMU: master branch
• nvme-cli: 2.3
• libnvme: 1.3
• fio: 3.33

I am currently using ZNS mode (run-zns.sh) and trace functions described here to figure out how FEMU works.

I found something goes wrong:

• NVMe actions (e.g., reset-zone, close-zone, zone-append) generated by nvme-cli are not captured in FEMU, which means that FEMU does not call related functions (traces are not printed). For example,
  • nvme_io_cmd is not called
  • sq->tail is not updated
  • ...

However, reports from nvme zns report-zones /dev/nvme0n1 shows correct results upon the actions. For example,

• when resetting zones, report shows that zones are reset.

(When reading and writing using fio, FEMU correctly calls related functions (traces are printed)).

---

Updated:

1. Sometimes, sq->tail is updated and related functions (e.g., zns_zone_append, zns_reset_zone) are called.

What I did:

• zones are reset (sudo blkzone reset /dev/nvme0n1) after executing multiple zone-append (echo "hello world" | sudo nvme zns zone-append /dev/nvme0n1 -z 512).

2. zns_reset_zone is called.

What I did:

• I executed sudo nvme zns reset-zone /dev/nvme0n1 multiple times (e.g., 200 times)

Why are not the functions in FEMU instantly called after executing a single command of nvme-cli?
(It seems that commands are batched before they are sent to the storage).

[huaicheng]

It depends on how often the nvme driver decides to ring the doorbell, not always synchronous for perf reasons. This is totally driver/software behavior, unrelated to FEMU.

[allencho1222]

Thank you for your quick response!