shmem_kernel_file_setup(9)

💖 shmem_kernel_file_setup(9) 💖

okay so bestie, welcome to the Kernel API Manual ✨ this one's about shmem_kernel_file_setup, and it's lowkey a whole vibe. it hands you an unlinked file that lives in tmpfs, and here's the thing — it must be kernel internal. no cap.

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🌸 NAME 🌸

shmem_kernel_file_setup — get an unlinked file living in tmpfs which must be kernel internal.

and listen, this part is important so pay attention 🫶 — there will be NO LSM permission checks against the underlying inode. none. zero. so anyone using this interface must do their LSM checks at a higher layer. the users are the big_key and shm implementations, and LSM checks are provided at the key or shm level rather than at the inode. periodt. 💅

⚠️ bestie please internalise this — no inode-level LSM checks happen here, so if you're the caller, the responsibility is yours at a higher layer. don't skip it. 💀

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✨ SYNOPSIS ✨

struct file * shmem_kernel_file_setup (const char *name , loff_t size ,
vma_flags_t flags );

like, that's the whole signature. she's simple, she's iconic 👑

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🎀 ARGUMENTS 🎀

• name — name for dentry (to be seen in /proc/<pid>/maps) 👀 so yes, it's gonna show up in the maps file, that's the whole point.
• size — size to be set for the file 🌸 that's your file size, set it, own it.
• flags — VMA_NORESERVE_BIT suppresses pre-accounting of the entire object size 💅 that's the specific flag bit and the specific behaviour, fr fr.

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🦋 SEE ALSO 🦋

Kernel file ./mm/shmem.c and honestly the whole shmem fam 👑

• shmem_recalc_inode(9)
• shmem_writeout(9)
• shmem_get_folio(9)
• shmem_file_setup(9)
• shmem_file_setup_with_mnt(9)
• shmem_zero_setup(9)
• shmem_zero_setup_desc(9)
• shmem_read_folio_gfp(9)

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💜 shoutout to ./mm for housing all of this, and this beauty is dated October 2026, filed under shmem_kernel_file_setup(9). mwah, go read the source bestie 😭💖