file_attr(2type)

✨ file_attr(2type) ✨

okay so bestie, this one is a type page (a 2type page, if we're being precise 💅) from section 2 of the Linux man-pages, and it's literally just the ✨glow-up✨ of a struct. no functions, no syscall, just a little bundle of fields that the kernel hands back and forth. it's giving "supporting cast member with main character energy" 🎀

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🌸 NAME 🌸

file_attr — filesystem file attributes 🦋

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💖 SYNOPSIS 💖

okay so first you gotta pull in the header:

#include <linux/fs.h>

and then here's the whole struct, character for character, no edits, we do not touch the struct, the struct is sacred 👑

struct file_attr {
     u64  fa_xflags;      // Extended flags
     u32  fa_extsize;     // Extent size hint
     u32  fa_nextents;    // Number of extents (read-only)
     u32  fa_projid;      // Project identifier
     u32  fa_cowextsize;  // CoW extent size hint
};

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🌈 DESCRIPTION 🌈

so like, this whole thing describes filesystem file attributes, and its literal job in life is to be the payload for two syscalls: file_getattr(2) and file_setattr(2). one reads it, one writes it. iconic teamwork fr fr 🫶

here's the field-by-field breakdown, no skips, no shortcuts:

• .fa_xflags — this is where the file attribute flags live. it's a bit mask, meaning it's zero or more of the FS_XFLAG_* flags OR'd together. the full menu is down in Flags below, iykyk ✨
• .fa_extsize — the extent size allocator hint, measured in bytes. basically it's a lil suggestion like "hey, for new allocations for this file, maybe prefer extents around this big?" a vibe check for the allocator, if you will 💅
• .fa_nextents — the number of data extents in the file, and bestie this one is read-only. file_getattr(2) fills it in for you; file_setattr(2) straight up ignores it. you don't write to this one, periodt 🚫
• .fa_projid — the project identifier. quota systems use it (quotactl(2)) to group files that belong together, like a lil friend group for accounting purposes 🌸
• .fa_cowextsize — the Copy-on-Write (CoW) extent size hint, in bytes. same deal as fa_extsize but specifically suggesting a preferred extent size for CoW operations 🦋

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🎀 Flags 🎀

here come the FS_XFLAG_* flags ok, deep breath, there's a bunch and we love them all:

• FS_XFLAG_REALTIME — data is stored in a realtime volume.
• FS_XFLAG_IMMUTABLE — file cannot be modified. (not "shouldn't", cannot. it's locked in 🔒)
• FS_XFLAG_APPEND — all writes must append to the end of the file.
• FS_XFLAG_SYNC — all writes are synchronous.
• FS_XFLAG_NOATIME — do not update file access time on reads.
• FS_XFLAG_NODUMP — do not include file in backups.
• FS_XFLAG_DAX — use Direct Access (DAX) for I/O operations.
• FS_XFLAG_NODEFRAG — exclude this file from defragmentation operations.
• FS_XFLAG_FILESTREAM — use filestream allocator for this file.
• FS_XFLAG_EXTSIZE — use the extent size hint from the fa_extsize field.
• FS_XFLAG_COWEXTSIZE — use the CoW extent size hint from the fa_cowextsize field.

📁 Directory-only flags:

these only make sense on directories, so don't come for them on files bestie:

• FS_XFLAG_RTINHERIT — new files created in this directory inherit the realtime flag.
• FS_XFLAG_NOSYMLINKS — disallow creation of symbolic links in this directory.
• FS_XFLAG_EXTSZINHERIT — new files created in this directory inherit the extent size hint.
• FS_XFLAG_PROJINHERIT — new files created in this directory inherit the project identifier.

👀 Read-only flags:

• FS_XFLAG_PREALLOC — file has preallocated extents.
• FS_XFLAG_HASATTR — file has extended attributes.
• FS_XFLAG_VERITY — file has fs-verity enabled.
• FS_XFLAG_CASEFOLD — the filesystem performs case-insensitive lookups (file and directory name comparisons ignore case).
• FS_XFLAG_CASENONPRESERVING — the filesystem does not preserve the case of file and directory names.

⚠️ and this part matters, so listen up: not all filesystems support all flags. setting unsupported flags may result in an error. so like, check before you go setting things, ok? don't just assume 🙈

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🕰️ HISTORY 🕰️

Linux v6.17

this structure is introduced. hello world, welcome to the kernel 👑

Linux v7.2

the FS_XFLAG_CASEFOLD and FS_XFLAG_CASENONPRESERVING are introduced, and the whole reason is so that upper layers — like NFSD — can retrieve case sensitivity information. slay ✨

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🔗 SEE ALSO 🔗

• file_getattr(2)
• file_setattr(2)

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and that's the whole page bestie, no cap 💖 this was Linux man-pages 6.20, dated 2026-10-11, and it's giving thorough. go read file_getattr(2) and file_setattr(2) next, they're the ones actually doing stuff. mwah 🫶💅