idr_alloc(9)

📦 version 7.3.1, in nixpkgs unstable

✨ idr_alloc(9) ✨

okay so bestie, welcome to the idr_alloc page from the Kernel API Manual — this is the one that hands out IDs like friendship bracelets at a sleepover 💅

🎀 NAME 🎀

idr_alloc — allocate an ID, bestie. that's the whole vibe. 💖

🦋 SYNOPSIS 🦋

int idr_alloc (struct idr *idr , void *ptr , int start , int end , gfp_t gfp );

🌸 ARGUMENTS 🌸

  • idr — the IDR handle. literally your whole little ID kingdom 👑
  • ptr — the pointer that gets associated with the brand-new ID. it's giving "these two are together now" 🫶
  • start — the minimum ID, and yes it's inclusive — so start itself is in the club 🎀
  • end — the maximum ID, but it's exclusive — sorry end, you're not on the list 🙈
  • gfp — memory allocation flags. the boring-but-essential paperwork ngl ⭐

💜 DESCRIPTION 💜

So what it actually does: it allocates an unused ID inside the range that start and end specify. lowkey simple, highkey useful ✨

And here's a cute little edge case for you: if end is <= 0, it gets treated as one larger than INT_MAX. that's the whole reason callers can just write start + N as the end value — as long as N is within integer range, you're golden 💖

⚠️ okay this part matters, don't skip it: the caller should provide their own locking to make sure two concurrent modifications to the IDR can't happen at the same time. no cap, that's on you.

Read-only accesses to the IDR are fine though — they may be done under the RCU read lock, or they may exclude simultaneous writers. pick your lane, both are valid 🦋

🔥 RETURN 🔥

  • the newly allocated ID — slay, you got one 🎉
  • -ENOMEM if memory allocation failed 😭
  • -ENOSPC if no free IDs could be found 💀

🌈 SEE ALSO 🌈

and that's the page, bestie!! 🧚 this lil gem lives in ./lib, dated October 2026, and it's filed under idr_alloc(9) — go forth and allocate responsibly 💜✨

📦 where this page comes from