STRUCT UBI_DEVICE_INFO(9)

💅 struct ubi_device_info(9) 💅

okay so this is a page from the Kernel API Manual and it's all about struct ubi_device_info — literally the little data structure that describes a UBI device 🦋

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✨ NAME ✨

struct ubi_device_info — the UBI device description data structure, bestie. that's it, that's the vibe 🎀

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🌸 SYNOPSIS 🌸

struct ubi_device_info {
    int ubi_num;
    int leb_size;
    int leb_start;
    int min_io_size;
    int max_write_size;
    int ro_mode;
    dev_t cdev;
 };

look at her. seven fields. main character energy 👑

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🫶 Members 🫶

• ubi_num — the ubi device number, like her little ID card 🪪
• leb_size — logical eraseblock size on this UBI device, so valid
• leb_start — where the logical eraseblocks kick off inside the physical eraseblocks (the starting offset, periodt)
• min_io_size — minimal I/O unit size. tiny but mighty ✨
• max_write_size — the max amount of bytes the underlying flash can write at one time (that's the MTD write buffer size, iykyk)
• ro_mode — flags whether this device is stuck in read-only mode 🙈
• cdev — the UBI character device major and minor numbers 💖

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💜 Description 💜

heads up: leb_size is the logical eraseblock size that the UBI device itself offers. but volumes of this UBI device may have a smaller logical eraseblock size if their alignment isn't equivalent to 1. so yeah, don't assume, ok? 💅

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so the max_write_size field is describing the flash write maximum write unit. example time: NOR flash lets you change individual bytes, so min_io_size is 1. but no cap, that does not mean NOR flash has to write data byte-by-byte 😭 instead, CFI NOR flashes have a write-buffer of, like, e.g., 64 bytes, and when they're writing large chunks of data they write 64-bytes at a time. obviously that improves write throughput — slay, efficiency 🔥

alsoooo, the MTD device may have N interleaved (striped) flash chips underneath it 👀 in that case min_io_size can be the physical min. I/O size of a single flash chip, while max_write_size can be N * min_io_size. math queen 🧮

and the max_write_size field is always greater or equivalent to min_io_size. e.g., some NOR flashes may have (min_io_size = 1, max_write_size = 64). in contrast, NAND flashes usually have min_io_size = max_write_size = NAND page size. iconic, consistent, no notes ⭐

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🎀 SEE ALSO 🎀

• Kernel file ./include/linux/mtd/ubi.h
• struct ubi_volume_info(9)
• struct ubi_sgl(9)
• ubi_sgl_init(9)

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ok that's the whole page bestie, go read the kernel file if you want more lore 🦋

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sign-off time 💫 this lil masterpiece lives in ./include/linux/mtd, it's dated October 2026, and it's filed under struct ubi_device_info(9) — mwah, bye 💋👑