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    SubjectRe: [PATCH] Added CONFIG_VFAT_FS_DUALNAMES option
    Date
    tridge@samba.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@samba.org>
    > Acked-by: Dave Kleikamp <shaggy@linux.vnet.ibm.com>
    > Acked-by: Paul E. McKenney <paulmck@linux.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@mail.parknet.co.jp>


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