usb_descriptor_fillbuf(9)

💅 usb_descriptor_fillbuf(9) — the Kernel API Manual glow-up ✨

okay bestie, so you're in the Linux kernel USB gadget world now, and this page is literally a gift from the kernel devs 🎀 this is usb_descriptor_fillbuf from the Kernel API Manual, and no cap, it's giving "tiny helper function that does exactly one thing and does it slay." let's get into it 💖

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🌸 NAME 🌸

usb_descriptor_fillbuf — fill buffer with descriptors ✨

like, the name really said what it needed to say. it fills a buffer. with descriptors. iconic behavior honestly 🫶

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🦋 SYNOPSIS 🦋

int usb_descriptor_fillbuf (void *buf , unsigned buflen , const struct
usb_descriptor_header **src );

three little arguments and an int coming back at you. that's it. that's the whole vibe check 💅

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💜 ARGUMENTS 💜

• buf — Buffer to be filled 🎀 this is the destination, the main character of the operation, the place where the descriptors are gonna live.
• buflen — Size of buf ✨ like, how much room the buffer actually has. gotta respect the boundaries, bestie.
• src — Array of descriptor pointers, terminated by null pointer. 🔥 so it's an array of pointers to descriptors, and it just keeps going until it hits that NULL — that null is the "ok we're done here" signal, the periodt of the array 💀

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🌈 DESCRIPTION 🌈

so what it does: it copies descriptors into the buffer, and it returns the length — OR a negative error code if they can't all be copied 😭 that's the whole contract, fr fr. copy succeeds → you get a length back. copy fails → negative error code, and you deal with it.

and when is this useful? the manpage says it's useful when assembling descriptors for an associated set of interfaces used as part of configuring a composite device 👑 — or, in other cases where sets of descriptors need to be marshaled 🦋 so basically: any time you've got a whole squad of descriptors that need to be packed together into one buffer, this is your girl. she marshals. she assembles. she ate 💅✨

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⭐ SEE ALSO ⭐

• Kernel file ./drivers/usb/gadget/config.c 🍓
• usb_copy_descriptors(9) 🧚

go read those too, iykyk 💖

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💀 friendly reminder from your girl: if the return value is negative, that means they could not all be copied. do not ignore it. do not pass go. check your lengths. 🫶

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and that's the whole page, bestie 🌸 this one came out of ./drivers/usb/gadget, dated October 2026, in the Kernel API Manual — go forth and marshal those descriptors 💜✨