By popular request, add a workaround that allows large (>128GB or so)

FAT32 filesystems to be mounted, subject to some fairly serious limitations.

This works by extending the internal pseudo-inode-numbers generated from
the file's starting cluster number to 64-bits, then creating a table
mapping these into arbitrary 32-bit inode numbers, which can fit in
struct dirent's d_fileno and struct vattr's va_fileid fields. The mappings
do not persist across unmounts or reboots, so it's not possible to export
these filesystems through NFS. The mapping table may grow to be rather
large, and may grow large enough to exhaust kernel memory on filesystems
with millions of files.

Don't enable this option unless you understand the consequences.

1 files changed, 23 insertions, 1 deletions

diff --git a/sys/fs/msdosfs/msdosfsmount.h b/sys/fs/msdosfs/msdosfsmount.h
index 0ff712f..46f9cc5 100644
--- a/sys/fs/msdosfs/msdosfsmount.h
+++ b/sys/fs/msdosfs/msdosfsmount.h
@@ -53,10 +53,14 @@
 
 #ifdef _KERNEL
 
+#include <sys/tree.h>
+
 #ifdef MALLOC_DECLARE
 MALLOC_DECLARE(M_MSDOSFSMNT);
 #endif
 
+struct msdosfs_fileno;
+
 /*
  * Layout of the mount control block for a msdos filesystem.
  */
@@ -99,7 +103,20 @@ struct msdosfsmount {
 	void *pm_w2u;	/* Unicode->Local iconv handle */
 	void *pm_u2d;	/* Unicode->DOS iconv handle */
 	void *pm_d2u;	/* DOS->Local iconv handle */
+	u_int32_t pm_nfileno;	/* next 32-bit fileno */
+	RB_HEAD(msdosfs_filenotree, msdosfs_fileno) pm_filenos; /* 64<->32-bit fileno mapping */
+};
+
+/*
+ * A 64-bit file number and the 32-bit file number to which it is mapped,
+ * in a red-black tree node.
+ */
+struct msdosfs_fileno {
+	RB_ENTRY(msdosfs_fileno)	mf_tree;
+	uint32_t			mf_fileno32;
+	uint64_t			mf_fileno64;
 };
+
 /* Byte offset in FAT on filesystem pmp, cluster cn */
 #define	FATOFS(pmp, cn)	((cn) * (pmp)->pm_fatmult / (pmp)->pm_fatdiv)
 
@@ -202,6 +219,10 @@ int msdosfs_init(struct vfsconf *vfsp);
 int msdosfs_uninit(struct vfsconf *vfsp);
 int msdosfs_mountroot(void);
 
+void msdosfs_fileno_init(struct mount *);
+void msdosfs_fileno_free(struct mount *);
+uint32_t msdosfs_fileno_map(struct mount *, uint64_t);
+
 #endif /* _KERNEL */
 
 /*
@@ -219,7 +240,7 @@ struct msdosfs_args {
 	char	*cs_win;	/* Windows(Unicode) Charset */
 	char	*cs_dos;	/* DOS Charset */
 	char	*cs_local;	/* Local Charset */
-	mode_t  dirmask;        /* dir  mask to be applied for msdosfs perms */
+	mode_t	dirmask;	/* dir  mask to be applied for msdosfs perms */
 };
 
 /*
@@ -236,6 +257,7 @@ struct msdosfs_args {
 #define	MSDOSFSMNT_RONLY	0x80000000	/* mounted read-only	*/
 #define	MSDOSFSMNT_WAITONFAT	0x40000000	/* mounted synchronous	*/
 #define	MSDOSFS_FATMIRROR	0x20000000	/* FAT is mirrored */
+#define	MSDOSFS_LARGEFS		0x10000000	/* perform fileno mapping */
 
 #define MSDOSFS_ARGSMAGIC	0xe4eff300