PMEM2_SOURCE_DEVICE_USC(3)

💖 pmem2_source_device_usc() 💖

okay bestie, so this one lives in the PMDK Programmer's Manual (yes, that PMDK, the persistent memory one, we're fancy now ✨) and it's literally the little function that tells you how many times your hardware got caught lacking during an unsafe shutdown. no cap.

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✨ NAME ✨

pmem2_source_device_usc() — returns the unsafe shutdown counter value of a device 🫶

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🌸 SYNOPSIS 🌸

#include <libpmem2.h>

struct pmem2_source;
int pmem2_source_device_usc(const struct pmem2_source *source, uint64_t *usc);

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🦋 DESCRIPTION 🦋

so the way that pmem2_source_device_usc() works is: it goes and grabs the sum of the unsafe shutdown count (USC) values of all hardware devices backing the data source, and then it drops that number into *usc. like, it's collecting receipts from every single device involved and adding them all up 💅

and listen — this is important — you can't just run around using this number however you feel. please refer to libpmem2_unsafe_shutdown(7) for the detailed description on how to properly consume this information. it's giving "read the instructions before you touch the thing", fr fr. 🙈

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👑 RETURN VALUE 👑

pmem2_source_device_usc() returns 0 on success. iconic. ✨

but if the function fails? then the content of the *usc variable is left unmodified (it does not get half-written, it does not get a vibe check, it stays exactly how you left it) and a negative error code is returned instead. 😭

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💀 ERRORS 💀

pmem2_source_device_usc() can fail with the following errors:

• PMEM2_E_NOSUPP — the underlying platform does not expose unsafe shutdown count information. so like, the info literally does not exist here, bestie, nothing we can do 💔
• -errno set by failing fstat(2), while trying to validate the file descriptor.
• -errno set by failing ndctl_new(), while trying to initiate a new NDCTL library context.
• -errno set by failing ndctl_dimm_get_dirty_shutdown(), while trying to obtain DIMM USC value.

bestie if you see any of those -errno ones, that means the underlying call flopped and the error number got handed straight back to you. go check errno(3), iykyk 🎀

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🌈 SEE ALSO 🌈

fstat(2), errno(3), malloc(3), libpmem2_unsafe_shutdown(7), and https://pmem.io 🔥

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okay that's the whole page, mwah 💜 this was the PMDK version, dated 2025-07-24 — go forth and check your unsafe shutdown counters responsibly, queen 👑💅