ecryptfs_write_headers_virt(9)

✨ ecryptfs_write_headers_virt(9) ✨

okay so bestie, we're in the Kernel API Manual today and this one is a whole little function about writing eCryptfs headers into memory. it's giving low-level, it's giving bytes, it's giving "trust me i know what i'm doing." let's get into it 💅

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🌸 NAME 🌸

ecryptfs_write_headers_virt — no description was given for this one in the original page, so we're just gonna sit here and stan the name itself. cute, concise, iconic. ✨

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🦋 SYNOPSIS 🦋

int ecryptfs_write_headers_virt (char *page_virt , size_t max , size_t
       *size , struct ecryptfs_crypt_stat *crypt_stat , struct dentry
       *ecryptfs_dentry );

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🎀 ARGUMENTS 🎀

• page_virt — the virtual address you're writing the headers to. like, this is where the bytes go, bestie 🫶
• max — the size of the memory that's been allocated at page_virt. know your limits, periodt.
• size — gets set to the number of bytes this function writes. it's the receipt for how much we actually used 💖
• crypt_stat — the cryptographic context. the main character of the crypto side of things 👑
• ecryptfs_dentry — the eCryptfs dentry. yes, that dentry 🦋

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💜 DESCRIPTION 💜

okay so here's the layout, and honestly it's a whole vibe. Format version: 1 ✨

🌈 Header Extent 🌈

• Octets 0-7: Unencrypted file size (big-endian)
• Octets 8-15: eCryptfs special marker
• Octets 16-19: Flags
  • Octet 16: File format version number (between 0 and 255)
  • Octets 17-18: Reserved
  • Octet 19:
    • Bit 1 (lsb): Reserved
    • Bit 2: Encrypted?
    • Bits 3-8: Reserved
• Octets 20-23: Header extent size (big-endian)
• Octets 24-25: Number of header extents at front of file (big-endian)
• Octet 26: Begin RFC 2440 authentication token packet set

🧚 Data Extent 🌈

• Data Extent 0: Lower data (CBC encrypted)
• Data Extent 1: Lower data (CBC encrypted)
• ... and it keeps going like that, no cap 💀

Returns zero on success. that's it, that's the win. slay 🌟

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🔥 SEE ALSO 🔥

Kernel file ./fs/ecryptfs/crypto.c — and the whole friend group:

• ecryptfs_from_hex(9)
• ecryptfs_derive_iv(9)
• ecryptfs_init_crypt_stat(9)
• ecryptfs_destroy_crypt_stat(9)
• virt_to_scatterlist(9)
• crypt_scatterlist(9)
• crypt_extent(9)
• ecryptfs_encrypt_page(9)
• ecryptfs_decrypt_page(9)
• ecryptfs_init_crypt_ctx(9)
• ecryptfs_copy_mount_wide_flags_to_inode_flags(9)
• ecryptfs_set_default_crypt_stat_vals(9)
• ecryptfs_new_file_context(9)
• ecryptfs_validate_marker(9)
• ecryptfs_process_flags(9)
• write_ecryptfs_marker(9)
• ecryptfs_code_for_cipher_string(9)
• ecryptfs_cipher_code_to_string(9)
• ecryptfs_write_metadata(9)
• set_default_header_data(9)
• ecryptfs_read_headers_virt(9)
• ecryptfs_read_xattr_region(9)
• ecryptfs_process_key_cipher(9)
• ecryptfs_destroy_crypto(9)
• ecryptfs_tfm_exists(9)
• ecryptfs_get_tfm_and_mutex_for_cipher_name(9)
• ecryptfs_encode_for_filename(9)
• ecryptfs_decode_from_filename(9)
• ecryptfs_encrypt_and_encode_filename(9)
• ecryptfs_decode_and_decrypt_filename(9)

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and that's the whole page, bestie!! this one lives in ./fs/ecryptfs and it's dated October 2026 — shoutout to ecryptfs_write_headers_virt(9) for being the blueprint. mwah 💋✨