STRUCT FILE(9)

💖 struct file(9) — like, the whole entire file vibe 💖

okay so this is struct file, from the Kernel API Manual, bestie — yes it's struct file(9) and yes it's a big deal. it's the thing that represents a file in the kernel, and we're gonna go through literally every single member together because i refuse to let you fail this vibe check 🫶

✨ SYNOPSIS ✨

here's the whole struct, exactly as it lives, don't touch anything:

struct file {
    spinlock_t f_lock;
    fmode_t f_mode;
    const struct file_operations    *f_op;
    struct address_space            *f_mapping;
    void *private_data;
    struct inode                    *f_inode;
    unsigned int                    f_flags;
    unsigned int                    f_iocb_flags;
    const struct cred               *f_cred;
    struct fown_struct              *f_owner;
    union {
      const struct path       f_path;
      struct path             __f_path;
    };
    union {
      struct mutex            f_pos_lock;
      u64 f_pipe;
    };
    loff_t f_pos;
  #ifdef CONFIG_SECURITY;
    void *f_security;
  #endif;
    errseq_t f_wb_err;
    errseq_t f_sb_err;
  #ifdef CONFIG_EPOLL;
    struct hlist_head               *f_ep;
  #endif;
    union {
      struct callback_head    f_task_work;
      struct llist_node       f_llist;
      struct file_ra_state    f_ra;
      freeptr_t f_freeptr;
    };
    file_ref_t f_ref;
 };

🌸 Members 🌸

• f_lock — a spinlock_t that protects f_ep and f_flags. huge caveat: it must not be taken from IRQ context. like, do not do that. periodt.
• f_mode — the FMODE_* flags, and these babies show up in hotpaths so treat them with respect 🔥
• f_op — the file operations. the whole personality of the file tbh.
• f_mapping — the contents of a cacheable, mappable object.
• private_data — filesystem or driver specific data. it's giving "your stuff goes here" ✨
• f_inode — the cached inode.
• f_flags — file flags.
• f_iocb_flags — iocb flags.
• f_cred — stashed credentials of whoever created/opened this file. lowkey the receipts 💅
• f_owner — file owner.
• {unnamed_union} — anonymous. (yes that's its whole description, we love a mysterious icon 🎀)
• f_path — path of the file.
• __f_path — writable alias for f_path, and listen: ONLY for core VFS, and only before the file gets open. no cap, do not go playing with this 🙈
• {unnamed_union} — anonymous. another one. iconic.
• f_pos_lock — the lock protecting the file position.
• f_pipe — specific to pipes 🍓
• f_pos — file position.
• f_security — LSM security context of this file. (only around when CONFIG_SECURITY is in the building)
• f_wb_err — writeback error.
• f_sb_err — per sb writeback errors.
• f_ep — link of all epoll hooks for this file. (hangs out only when CONFIG_EPOLL says so)
• {unnamed_union} — anonymous. third one, slay.
• f_task_work — task work entry point.
• f_llist — work queue entrypoint.
• f_ra — the file's readahead state.
• f_freeptr — pointer used by the SLAB_TYPESAFE_BY_RCU file cache — and bestie, don't touch. literally. do not.
• f_ref — reference count. the main character of lifetime management fr fr 👑

👀 SEE ALSO 👀

Kernel file ./include/linux/fs.h — plus, like, a whole friend group of cross-references:

• enum positive_aop_returns(9)
• struct address_space(9)
• struct file_ra_state(9)
• i_uid_into_vfsuid(9)
• i_uid_needs_update(9)
• i_uid_update(9)
• i_gid_into_vfsgid(9)
• i_gid_needs_update(9)
• i_gid_update(9)
• inode_fsuid_set(9)
• inode_fsgid_set(9)
• fsuidgid_has_mapping(9)
• inode_set_ctime(9)
• file_write_started(9)
• file_write_not_started(9)
• struct renamedata(9)
• is_mgtime(9)
• iput_if_not_last(9)
• is_idmapped_mnt(9)
• file_start_write(9)
• file_end_write(9)
• kiocb_start_write(9)
• kiocb_end_write(9)
• name_is_dot_dotdot(9)
• name_contains_dotdot(9)
• inode_dio_begin(9)
• inode_dio_end(9)
• generic_ci_validate_strict_name(9)

okay that's the whole page, every last flag and field accounted for 💜 this one came from ./include/linux and it's dated October 2026 — so yeah, go forth and read those struct files, bestie, you ate 🎀✨