sg_split(9)

🌸 sg_split(9) — the Kernel API Manual moment

okay so this is sg_split, from the kernel API manual, and yes bestie the (9) means it's a kernel-internal function, we're in the deep deep. no cap, this one is genuinely useful and also genuinely a little fiddly. let's get into it 💅

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✨ NAME ✨

sg_split — split a scatterlist into several scatterlists. that's it, that's the vibe. one sg list goes in, several sg lists come out. 🎀

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🦋 SYNOPSIS 🦋

int sg_split (struct scatterlist *in , const int in_mapped_nents , const
       off_t skip , const int nb_splits , const size_t *split_sizes , struct
       scatterlist **out , int *out_mapped_nents , gfp_t gfp_mask );

like, look at all those params. main character energy honestly. 🌈

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💖 ARGUMENTS 💖

okay bestie, let's meet the cast:

• in — the input sg list. the thing we're chopping up. ✂️
• in_mapped_nents — the result of a dma_map_sg(in, ...), or 0 if it's not mapped. so: the count you got back from mapping, or a big fat zero if no mapping happened.
• skip — the number of bytes to skip in the input sg list. like scrolling past the intro, but in bytes. 🙈
• nb_splits — the number of desired sg outputs. how many pieces we're making, bestie.
• split_sizes — the respective size of each output sg list in bytes. one size per output, in order. 📏
• out — an array where to store the allocated output sg lists. this is where the magic lands. ✨
• out_mapped_nents — the resulting sg lists mapped number of sg entries. Might be NULL if sglist not already mapped (in_mapped_nents = 0). ⚠️ so like, if you didn't map it, pass NULL here, fr fr.
• gfp_mask — the allocation flag. the classic gfp_t situation, you know the drill. 🫶

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🔥 DESCRIPTION 🔥

This function splits the input sg list into nb_splits sg lists, which are allocated and stored into out. The in is split into:

• out[0], which covers bytes [skip .. skip + split_sizes[0] - 1] of in
• out[1], which covers bytes [skip + split_sizes[0] .. skip + split_sizes[0] + split_sizes[1] -1] etc ...

so yeah, each output picks up exactly where the last one left off, offset by skip at the start. mathematically tidy, we love to see it. 🧚

⚠️ heads up bestie: It will be the caller's duty to kfree out array members. not mine, not the function's — yours. the allocated output sg lists in out are your responsibility now. don't be the person who leaks them, i'm begging. 😭

Returns 0 upon success, or error code. so, 0 = slay, anything else = read the error code and cry a little. 💀

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👑 SEE ALSO 👑

Kernel file ./lib/sg_split.c — go read the source, iykyk. that's where the real lore lives. ⭐

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okay that's the whole page, bestie! written from the ./lib corner of the kernel, October 2026 edition. go split some scatterlists and remember to kfree 💜🫶🌷