do_shrink(9)

💅 do_shrink — make a file smaller (yes, literally that) 🎀

okay so this is a page from the Kernel API Manual, and it's about do_shrink(9). bestie, the name is not mysterious: it makes a file smaller. that's the whole gig. let's go ✨

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🌸 SYNOPSIS 🌸

int do_shrink (struct inode *inode , u64 newsize );

that's it, that's the signature. two args, one int coming back at you 🫶

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🦋 ARGUMENTS 🦋

• inode — the inode. yeah. the inode. the one we're shrinking. 👑
• newsize — the size to make the file. that's the target size, the goal, the destination, the moment 💫

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💖 DESCRIPTION 💖

so here's the vibe check: this function is called with an exclusive lock on inode. exclusive. no sharing, no plus-ones, nobody else touching this inode while we're working. 🔒

and the rule, the one non-negotiable rule: the size must be equal to or smaller than the current inode size. equal is fine. smaller is fine. bigger? absolutely not, that's not shrinking, that's a whole different function (do_grow(9) is right there in SEE ALSO, iykyk 😌).

no cap, if you're coming in here trying to make a file bigger, you have misunderstood the assignment 💀

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⭐ RETURN ⭐

errno — that's the return value. periodt.

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🌈 SEE ALSO 🌈

it's giving extended universe, honestly. the whole bmap.c friend group shows up:

• the kernel file ./fs/gfs2/bmap.c
• gfs2_unstuffer_folio(9)
• gfs2_unstuff_dinode(9)
• find_metapath(9)
• metaptr1(9)
• metapointer(9)
• lookup_metapath(9)
• fillup_metapath(9)
• gfs2_extent_length(9)
• gfs2_hole_size(9)
• __gfs2_iomap_alloc(9)
• gfs2_alloc_size(9)
• __gfs2_iomap_get(9)
• gfs2_block_map(9)
• gfs2_journaled_truncate(9)
• sweep_bh_for_rgrps(9)
• find_nonnull_ptr(9)
• punch_hole(9)
• do_grow(9)
• gfs2_setattr_size(9)
• gfs2_free_journal_extents(9)
• gfs2_add_jextent(9)
• gfs2_map_journal_extents(9)
• gfs2_write_alloc_required(9)

like, the entire roster. main character energy from every single one of them 💅

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and that's the page!! mwah 🍓 this one came out of ./fs/gfs2, dated October 2026, and it's filed under do_shrink(9). go shrink something (smaller than it is now, PLEASE, we went over this 😭) 💜