linux-kernel - Re: [PATCH v8 01/13] exfat: add in-memory and on-disk structures and headers

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Date:   Thu, 2 Jan 2020 20:11:37 +0900
From:   Namjae Jeon <linkinjeon@...il.com>
To:     Pali Rohár <pali.rohar@...il.com>
Cc:     Namjae Jeon <namjae.jeon@...sung.com>,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        gregkh@...uxfoundation.org, valdis.kletnieks@...edu, hch@....de,
        sj1557.seo@...sung.com
Subject: Re: [PATCH v8 01/13] exfat: add in-memory and on-disk structures and headers

2020-01-02 20:06 GMT+09:00, Pali Rohár <pali.rohar@...il.com>:
> Hello, just remainder for question below, so it would not be lost.
>
> I guess that if comment for structure says that it needs to have exact
> size then structure should be marked as packed to prevent any unexpected
> paddings added by compiler (as IIRC compiler is free to add any padding
> between any structure members).
Okay, I will fix it on next version.

Thanks!
>
> On Sunday 29 December 2019 15:11:08 Pali Rohár wrote:
>> On Friday 20 December 2019 01:24:07 Namjae Jeon wrote:
>> > +
>> > +#define JUMP_BOOT_LEN			3
>> > +#define OEM_NAME_LEN			8
>> > +#define MUST_BE_ZERO_LEN		53
>> > +#define EXFAT_FILE_NAME_LEN		15
>> > +
>> > +/* EXFAT BIOS parameter block (64 bytes) */
>> > +struct bpb64 {
>> > +	__u8 jmp_boot[JUMP_BOOT_LEN];
>> > +	__u8 oem_name[OEM_NAME_LEN];
>> > +	__u8 res_zero[MUST_BE_ZERO_LEN];
>> > +};
>> > +
>> > +/* EXFAT EXTEND BIOS parameter block (56 bytes) */
>> > +struct bsx64 {
>> > +	__le64 vol_offset;
>> > +	__le64 vol_length;
>> > +	__le32 fat_offset;
>> > +	__le32 fat_length;
>> > +	__le32 clu_offset;
>> > +	__le32 clu_count;
>> > +	__le32 root_cluster;
>> > +	__le32 vol_serial;
>> > +	__u8 fs_version[2];
>> > +	__le16 vol_flags;
>> > +	__u8 sect_size_bits;
>> > +	__u8 sect_per_clus_bits;
>> > +	__u8 num_fats;
>> > +	__u8 phy_drv_no;
>> > +	__u8 perc_in_use;
>> > +	__u8 reserved2[7];
>> > +};
>>
>> Should not be this structure marked as packed? Also those two below.
>>
>> > +/* EXFAT PBR[BPB+BSX] (120 bytes) */
>> > +struct pbr64 {
>> > +	struct bpb64 bpb;
>> > +	struct bsx64 bsx;
>> > +};
>> > +
>> > +/* Common PBR[Partition Boot Record] (512 bytes) */
>> > +struct pbr {
>> > +	union {
>> > +		__u8 raw[64];
>> > +		struct bpb64 f64;
>> > +	} bpb;
>> > +	union {
>> > +		__u8 raw[56];
>> > +		struct bsx64 f64;
>> > +	} bsx;
>> > +	__u8 boot_code[390];
>> > +	__le16 signature;
>> > +};
>>
>
> --
> Pali Rohár
> pali.rohar@...il.com
>