[RFC][FAT] Handle MBR on the first sector
Franck Jullien
franck.jullien at gmail.com
Fri Sep 14 03:22:07 EDT 2012
2012/9/14 Sascha Hauer <s.hauer at pengutronix.de>:
> Hi Franck,
>
> On Thu, Sep 13, 2012 at 02:13:29PM +0200, Franck Jullien wrote:
>> *** Did not send this email with git because it's no working where I am **
>>
>> We may have some disk with MBR as a first sector. In this case, the
>> current FAT check returns an error. However, the FAT sector exist and
>> the MBR can tell us where it is.
>>
>> This patch make the FAT fs try to find the FAT boot sector on the first
>> sector of the first partition in case it is not on sector 0.
>
> The patch looks good. Not applying it because it's RFC, but I would if
> you give your ok.
>
You have it.
> Sascha
>
>>
>> Signed-off-by: Franck Jullien <franck.jullien at gmail.com>
>> ---
>> fs/fat/ff.c | 24 ++++++++++++++++++++----
>> 1 files changed, 20 insertions(+), 4 deletions(-)
>>
>> diff --git a/fs/fat/ff.c b/fs/fat/ff.c
>> index 66db1d6..6a4ae32 100644
>> --- a/fs/fat/ff.c
>> +++ b/fs/fat/ff.c
>> @@ -191,6 +191,7 @@
>> #define FSI_Nxt_Free 492 /* FSI: Last allocated cluster (4) */
>> #define MBR_Table 446 /* MBR: Partition table offset (2) */
>> #define SZ_PTE 16 /* MBR: Size of a partition table entry */
>> +#define MBR_StartSector 8 /* MBR: Offset of Starting Sector in
>> Partition Table Entry */
>> #define BS_55AA 510 /* Boot sector signature (2) */
>>
>> #define DIR_Name 0 /* Short file name (11) */
>> @@ -1533,11 +1534,15 @@ int follow_path ( /* 0(0): successful, !=0:
>> error code */
>> */
>> static int check_fs ( /* 0:The FAT BR, 1:Valid BR but not an FAT,
>> 2:Not a BR, 3:Disk error */
>> FATFS *fs, /* File system object */
>> - DWORD sect /* Sector# (lba) to check if it is an FAT boot record or not */
>> + DWORD sect, /* Sector# (lba) to check if it is an FAT boot record or not */
>> + DWORD *bootsec
>> )
>> {
>> int ret;
>>
>> + if(bootsec)
>> + *bootsec = 0;
>> +
>> /* Load boot record */
>> ret = disk_read(fs, fs->win, sect, 1);
>> if (ret)
>> @@ -1553,6 +1558,12 @@ static int check_fs ( /* 0:The FAT BR, 1:Valid
>> BR but not an FAT, 2:Not a BR, 3:
>> if ((LD_DWORD(&fs->win[BS_FilSysType32]) & 0xFFFFFF) == 0x544146)
>> return 0;
>>
>> + if(bootsec)
>> + /* This must be an MBR, so return the starting sector of the
>> + * first partition so we could check if there is a FAT boot
>> + * sector there */
>> + *bootsec = LD_WORD(&fs->win[MBR_Table + MBR_StartSector]);
>> +
>> return -ENODEV;
>> }
>>
>> @@ -1565,6 +1576,7 @@ static int chk_mounted ( /* 0(0): successful,
>> !=0: any error occurred */
>> )
>> {
>> BYTE fmt, b;
>> + DWORD first_boot_sect;
>> DWORD bsect, fasize, tsect, sysect, nclst, szbfat;
>> WORD nrsv;
>>
>> @@ -1579,9 +1591,13 @@ static int chk_mounted ( /* 0(0): successful,
>> !=0: any error occurred */
>> return -EIO;
>> #endif
>> /* Search FAT partition on the drive. Supports only generic
>> partitionings, FDISK and SFD. */
>> - fmt = check_fs(fs, bsect = 0); /* Check sector 0 if it is a VBR */
>> - if (fmt)
>> - return fmt; /* No FAT volume is found */
>> + fmt = check_fs(fs, bsect = 0, &first_boot_sect); /* Check sector 0
>> if it is a VBR */
>> + if (fmt && first_boot_sect != 0) {
>> + /* Sector 0 is an MBR, now check for FAT in the first partition */
>> + fmt = check_fs(fs, bsect = first_boot_sect, NULL);
>> + if(fmt)
>> + return fmt; /* No FAT volume is found */
>> + }
>>
>> /* Following code initializes the file system object */
>>
>> --
>> 1.7.1
>>
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>
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