On 2021-01-13 20:51, 常廉志 wrote: >> On 2021-01-11 23:53, lianzhi chang wrote: >> >>>> When the capacity of the disc is too large (assuming the 4.7G >>>> specification), the disc (UDF file system) will be burned >>>> multiple times in the windows (Multisession Usage). When the >>>> remaining capacity of the CD is less than 300M (estimated >>>> value, for reference only), open the CD in the Linux system, >>>> the content of the CD is displayed as blank (the kernel will >>>> say "No VRS found"). Windows can display the contents of the >>>> CD normally. >>>> Through analysis, in the "fs/udf/super.c": udf_check_vsd >>>> function, the actual value of VSD_MAX_SECTOR_OFFSET may >>>> be much larger than 0x800000. According to the current code >>> l>ogic, it is found that the type of sbi->s_session is "__s32", >>>> when the remaining capacity of the disc is less than 300M >>>> (take a set of test values: sector=3154903040, >>>> sbi->s_session=1540464, sb->s_blocksize_bits=11 ), the >>>> calculation result of "sbi->s_session << sb->s_blocksize_bits" >>>> will overflow. Therefore, it is necessary to convert the >>>> type of s_session to "loff_t" (when udf_check_vsd starts, >>>> assign a value to _sector, which is also converted in this >>>> way), so that the result will not overflow, and then the >>>> content of the disc can be displayed normally. >>>> >>> Signed-off-by: lianzhi chang <changlian...@uniontech.com> >>>> --- >>>> fs/udf/super.c | 2 +- >>>> 1 file changed, 1 insertion(+), 1 deletion(-) >>>> >>>> diff --git a/fs/udf/super.c b/fs/udf/super.c >>>> index 5bef3a68395d..6c3069cd1321 100644 >>>> --- a/fs/udf/super.c >>>> +++ b/fs/udf/super.c >>>> @@ -757,7 +757,7 @@ static int udf_check_vsd(struct super_block *sb) >>>> >>>> if (nsr > 0) >>>> return 1; >>>> - else if (!bh && sector - (sbi->s_session << sb->s_blocksize_bits) >>>> == >>>> + else if (!bh && sector - ((loff_t)sbi->s_session << >>>> sb->s_blocksize_bits) == >>>> VSD_FIRST_SECTOR_OFFSET) >>>> return -1; >>>> else >>> >>> >>> Looks good. Perhaps consider factoring out the conversion (which also >>> occurs >>> earlier in the function) so that the complexity of this "else if" can >>> be >>> reduced? >>> >> >>> Reviewed-by: Steven J. Magnani <magnani@xxxxxxxx> >> >> Thank you very much! So, which one of the following methods do you >> think is better: >> >> (1) Change the type of s_session in struct udf_sb_info to __s64. If you >> modify this way, it may involve some memory copy problems of the >> structure, and there are more modifications. >> >> (2) Definition: loff_t sector_offset=sbi->s_session << >> sb->s_blocksize_bits, and then put sector_offset into the "else if" >> statement. >> >> (3) Or is there any other better way?
>I had #2 in mind. >------------------------------------------------------------------------ > Steven J. Magnani "I claim this network for MARS! Thank you very much for your suggestion, I will submit a new patch
