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Date: Sat, 27 Jun 2009 10:56:02 +0900
From: OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
To: tridge@...ba.org
Cc: john.lanza@...ux.com, linux-kernel@...r.kernel.org,
linux-fsdevel@...r.kernel.org,
Dave Kleikamp <shaggy@...ux.vnet.ibm.com>,
Steve French <sfrench@...ibm.com>,
Mingming Cao <cmm@...ibm.com>,
Paul McKenney <paulmck@...ux.vnet.ibm.com>
Subject: Re: [PATCH] Added CONFIG_VFAT_FS_DUALNAMES option
tridge@...ba.org writes:
> This is a new patch for VFAT long filename support, replacing the one
> that I posted last month. It retains a lot more functionality then the
> previous patch.
>
> A FAQ will be posted immediately after this patch to answer the
> questions that were raised from the previous discussion.
Looks good to me. It seems to be trying to be minimal change, and I
guess it would be worth a try for realworld problem. Like FAQ is
saying, the default might be arguable though.
> When VFAT_FS_DUALNAMES is disabled we avoid the creation of 8.3 short
> filenames for files on VFAT filesystems that require a long name. The
> patch uses a pattern of 11 bytes in the directory entry which contains
> invalid characters such that it cannot be considered to be a valid short
> filename.
>
> Signed-off-by: Andrew Tridgell <tridge@...ba.org>
> Acked-by: Dave Kleikamp <shaggy@...ux.vnet.ibm.com>
> Acked-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> ---
> fs/fat/Kconfig | 20 +++++++++++++++++
> fs/fat/dir.c | 15 ++++++-------
> fs/fat/namei_vfat.c | 59 +++++++++++++++++++++++++++++++++++++++++++++++++++
> 3 files changed, 86 insertions(+), 8 deletions(-)
>
> diff --git a/fs/fat/Kconfig b/fs/fat/Kconfig
> index 182f9ff..907a5de 100644
> --- a/fs/fat/Kconfig
> +++ b/fs/fat/Kconfig
> @@ -74,6 +74,26 @@ config VFAT_FS
> To compile this as a module, choose M here: the module will be called
> vfat.
>
> +config VFAT_FS_DUALNAMES
> + bool "VFAT dual names support"
> + depends on VFAT_FS
> + help
> + This option provides support for dual filenames on VFAT filesystems.
> + If this option is disabled then file creation will either put
> + a short (8.3) name or a long name on the file, but never both.
> + The field where a shortname would normally go is filled with
> + invalid characters such that it cannot be considered a valid
> + short filename.
> +
> + That means that long filenames created with this option
> + disabled will not be accessible at all to operating systems
> + that do not understand the VFAT extensions.
> +
> + Users considering enabling this option should consider the implications
> + of any patents that may exist on dual filenames in VFAT.
> +
> + If unsure, say N
> +
> config FAT_DEFAULT_CODEPAGE
> int "Default codepage for FAT"
> depends on MSDOS_FS || VFAT_FS
> diff --git a/fs/fat/dir.c b/fs/fat/dir.c
> index 38ff75a..cd5d3ec 100644
> --- a/fs/fat/dir.c
> +++ b/fs/fat/dir.c
> @@ -420,14 +420,13 @@ parse_record:
> }
> i += chl;
> }
> - if (!last_u)
> - continue;
> -
> - /* Compare shortname */
> - bufuname[last_u] = 0x0000;
> - len = fat_uni_to_x8(sbi, bufuname, bufname, sizeof(bufname));
> - if (fat_name_match(sbi, name, name_len, bufname, len))
> - goto found;
> + if (last_u) {
> + /* Compare shortname */
> + bufuname[last_u] = 0x0000;
> + len = fat_uni_to_x8(sbi, bufuname, bufname, sizeof(bufname));
> + if (fat_name_match(sbi, name, name_len, bufname, len))
> + goto found;
> + }
>
> if (nr_slots) {
> void *longname = unicode + FAT_MAX_UNI_CHARS;
> diff --git a/fs/fat/namei_vfat.c b/fs/fat/namei_vfat.c
> index 73471b7..894f44d 100644
> --- a/fs/fat/namei_vfat.c
> +++ b/fs/fat/namei_vfat.c
> @@ -22,6 +22,7 @@
> #include <linux/smp_lock.h>
> #include <linux/buffer_head.h>
> #include <linux/namei.h>
> +#include <linux/random.h>
> #include "fat.h"
>
> /*
> @@ -586,6 +587,59 @@ xlate_to_uni(const unsigned char *name, int len, unsigned char *outname,
> return 0;
> }
>
> +#ifndef CONFIG_VFAT_FS_DUALNAMES
> +/*
> + * build a 11 byte 8.3 buffer which is not a short filename. We want 11
> + * bytes which:
> + * - will be seen as a constant string to all APIs on Linux and Windows
> + * - cannot be matched with wildcard patterns
> + * - cannot be used to access the file
> + * - has a low probability of collision within a directory
> + * - has an invalid 3 byte extension
> + * - contains at least one non-space and non-nul byte
> + */
> +static void vfat_build_dummy_83_buffer(struct inode *dir, char *msdos_name)
> +{
> + u32 rand_num = random32() & 0x3FFFFFFF;
> + int i;
> +
> + /* a value of zero would leave us with only nul and spaces,
> + * which would not work with older linux systems
> + */
> + if (rand_num == 0)
> + rand_num = 1;
> +
> + /* we start with a space followed by nul as spaces at the
> + * start of an entry are trimmed in FAT, which means that
> + * starting the 11 bytes with 0x20 0x00 gives us a value which
> + * cannot be used to access the file. It also means that the
> + * value as seen from all Windows and Linux APIs is a constant
> + */
> + msdos_name[0] = ' ';
> + msdos_name[1] = 0;
> +
> + /* we use / and 2 nul bytes for the extension. These are
> + * invalid in FAT and mean that utilities that show the
> + * directory show no extension, but still work via the long
> + * name for old Linux kernels
> + */
> + msdos_name[8] = '/';
> + msdos_name[9] = 0;
> + msdos_name[10] = 0;
> +
> + /*
> + * fill the remaining 6 bytes with random invalid values
> + * This gives us a low collision rate, which means a low
> + * chance of problems with chkdsk.exe and WindowsXP
> + */
> + for (i = 2; i < 8; i++) {
> + msdos_name[i] = rand_num & 0x1F;
> + rand_num >>= 5;
> + }
> +}
> +#endif
> +
> +
> static int vfat_build_slots(struct inode *dir, const unsigned char *name,
> int len, int is_dir, int cluster,
> struct timespec *ts,
> @@ -628,6 +682,11 @@ static int vfat_build_slots(struct inode *dir, const unsigned char *name,
> goto shortname;
> }
>
> +#ifndef CONFIG_VFAT_FS_DUALNAMES
> + vfat_build_dummy_83_buffer(dir, msdos_name);
> + lcase = 0;
> +#endif
> +
> /* build the entry of long file name */
> cksum = fat_checksum(msdos_name);
--
OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
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