file-systems: Add support for F2FS.

* gnu/build/file-systems.scm (%f2fs-endianness): New syntax.
(f2fs-superblock?, read-f2fs-superblock, f2fs-superblock-uuid)
(f2fs-superblock-volume-name, check-f2fs-file-system): New procedures.
(%partition-label-readers, %partition-uuid-readers, check-file-system): Register them.

Signed-off-by: Danny Milosavljevic <dannym@scratchpost.org>

1 files changed, 59 insertions, 2 deletions

diff --git a/gnu/build/file-systems.scm b/gnu/build/file-systems.scm
index 902563b219..bbea4c766e 100644
--- a/gnu/build/file-systems.scm
+++ b/gnu/build/file-systems.scm
@@ -338,6 +338,58 @@ if DEVICE does not contain a JFS file system."
 
 
 ;;;
+;;; F2FS (Flash-Friendly File System)
+;;;
+
+;;; https://git.kernel.org/pub/scm/linux/kernel/git/jaegeuk/f2fs.git/tree/include/linux/f2fs_fs.h
+;;; (but using xxd proved to be simpler)
+
+(define-syntax %f2fs-endianness
+  ;; Endianness of F2FS file systems
+  (identifier-syntax (endianness little)))
+
+;; F2FS actually stores two adjacent copies of the superblock.
+;; should we read both?
+(define (f2fs-superblock? sblock)
+  "Return #t when SBLOCK is an F2FS superblock."
+  (let ((magic (bytevector-u32-ref sblock 0 %f2fs-endianness)))
+    (= magic #xF2F52010)))
+
+(define (read-f2fs-superblock device)
+  "Return the raw contents of DEVICE's F2FS superblock as a bytevector, or #f
+if DEVICE does not contain an F2FS file system."
+  (read-superblock device
+                   ;; offset of magic in first copy
+                   #x400
+                   ;; difference between magic of second
+                   ;; and first copies
+                   (- #x1400 #x400)
+                   f2fs-superblock?))
+
+(define (f2fs-superblock-uuid sblock)
+  "Return the UUID of F2FS superblock SBLOCK as a 16-byte bytevector."
+  (sub-bytevector sblock
+                  (- (+ #x460 12)
+                     ;; subtract superblock offset
+                     #x400)
+                  16))
+
+(define (f2fs-superblock-volume-name sblock)
+  "Return the volume name of SBLOCK as a string of at most 512 characters, or
+#f if SBLOCK has no volume name."
+  (utf16->string (sub-bytevector sblock (- (+ #x470 12) #x400) 512) %f2fs-endianness))
+
+(define (check-f2fs-file-system device)
+  "Return the health of a F2FS file system on DEVICE."
+  (match (status:exit-val
+          (system* "fsck.f2fs" "-p" device))
+    ;; 0 and -1 are the only two possibilities
+    ;; (according to the manpage)
+    (0 'pass)
+    (_ 'fatal-error)))
+
+
+;;;
 ;;; LUKS encrypted devices.
 ;;;
 
@@ -472,7 +524,9 @@ partition field reader that returned a value."
         (partition-field-reader read-fat16-superblock
                                 fat16-superblock-volume-name)
         (partition-field-reader read-jfs-superblock
-                                jfs-superblock-volume-name)))
+                                jfs-superblock-volume-name)
+        (partition-field-reader read-f2fs-superblock
+                                f2fs-superblock-volume-name)))
 
 (define %partition-uuid-readers
   (list (partition-field-reader read-iso9660-superblock
@@ -486,7 +540,9 @@ partition field reader that returned a value."
         (partition-field-reader read-fat16-superblock
                                 fat16-superblock-uuid)
         (partition-field-reader read-jfs-superblock
-                                jfs-superblock-uuid)))
+                                jfs-superblock-uuid)
+        (partition-field-reader read-f2fs-superblock
+                                f2fs-superblock-uuid)))
 
 (define read-partition-label
   (cut read-partition-field <> %partition-label-readers))
@@ -582,6 +638,7 @@ were found."
      ((string-prefix? "btrfs" type) check-btrfs-file-system)
      ((string-suffix? "fat" type) check-fat-file-system)
      ((string-prefix? "jfs" type) check-jfs-file-system)
+     ((string-prefix? "f2fs" type) check-f2fs-file-system)
      ((string-prefix? "nfs" type) (const 'pass))
      (else #f)))