_shift_data_left_pages(9)

🌸 _shift_data_left_pages — a Kernel API Manual moment 🌸

okay bestie, so this is a page from the Kernel API Manual (that's the (9) bit, section 9, kernel developer vibes 💅). It's called _shift_data_left_pages and honestly? It's giving "small but mighty helper function" energy. Let's get into it 🫶

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✨ NAME ✨

_shift_data_left_pages —

so like… the original page literally leaves this blank after the dash 😭 no cap, there's no description here. We move on. Main character energy is elsewhere, iykyk.

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🦋 SYNOPSIS 🦋

void _shift_data_left_pages (struct page **pages , size_t pgto_base ,
size_t pgfrom_base , size_t len );

that's the whole vibe: returns void, so it's not gonna hand you anything back. It just does the thing 💫

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💖 ARGUMENTS 💖

• pages — the vector of pages holding both the source and the dest memory area. like, one big friend group of pages, both sides living in it 💀
• pgto_base — the page vector address of the destination (where the data is heading 🏃‍♀️)
• pgfrom_base — the page vector address of the source (where the data's coming from ✨)
• len — the number of bytes to copy, bestie. count 'em. 📏

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🎀 NOTE 🎀

okay this part matters, so listen up 👑

the addresses pgto_base and pgfrom_base are both calculated in the same way: if a memory area starts at byte base in page pages[i], then its address is given as:

(i << PAGE_CACHE_SHIFT) + base

also note (and this is the important bit, ngl): pgto_base must be < pgfrom_base — like, that's a hard requirement, not a suggestion 🔥 but the memory areas they point to may overlap. so the addresses are ordered, the actual memory doesn't have to be. iconic, honestly.

🚨 read that again, bestie: pgto_base must be less than pgfrom_base. don't come crying to me if you flip them 💀

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🌈 SEE ALSO 🌈

this is a whole friend group, fr fr — all from the kernel file ./net/sunrpc/xdr.c:

• xdr_encode_opaque_fixed(9)
• xdr_encode_opaque(9)
• xdr_terminate_string(9)
• xdr_buf_to_bvec(9)
• xdr_buf_to_sg(9)
• xdr_buf_to_sg_alloc(9)
• xdr_inline_pages(9)
• _shift_data_right_pages(9)
• _copy_to_pages(9)
• _copy_from_pages(9)
• xdr_buf_pages_zero(9)
• xdr_shrink_bufhead(9)
• xdr_shrink_pagelen(9)
• xdr_stream_pos(9)
• xdr_page_pos(9)
• xdr_init_encode(9)
• xdr_init_encode_pages(9)
• __xdr_commit_encode(9)
• xdr_reserve_space(9)
• xdr_reserve_space_vec(9)
• xdr_truncate_encode(9)
• xdr_truncate_decode(9)
• xdr_restrict_buflen(9)
• xdr_write_pages(9)
• xdr_init_decode(9)
• xdr_init_decode_pages(9)
• xdr_finish_decode(9)
• xdr_inline_decode(9)
• xdr_read_pages(9)
• xdr_set_pagelen(9)
• xdr_enter_page(9)
• xdr_buf_subsegment(9)
• xdr_stream_subsegment(9)
• xdr_stream_move_subsegment(9)
• xdr_stream_zero(9)
• xdr_buf_trim(9)
• xdr_stream_decode_string_dup(9)
• xdr_stream_decode_opaque_auth(9)
• xdr_stream_encode_opaque_auth(9)

like, that's a lot of siblings. go say hi to _shift_data_right_pages(9) especially, it's literally the mirror twin 🪞

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and that's the whole page, bestie 🎀 sign-off time: this one lives in ./net/sunrpc, dated October 2026, and it's filed under _shift_data_left_pages(9). slay, go shift some data. leftwards. 💜✨