[PATCH 1/3] base-files: sysupgrade: add tar.sh with helpers for building archives

[Rafał Miłecki]

On 26.02.2024 22:27, Paul D wrote:
>> diff --git a/package/base-files/files/lib/upgrade/tar.sh b/package/base-files/files/lib/upgrade/tar.sh
>> new file mode 100644
>> index 0000000000..00057dd760
>> --- /dev/null
>> +++ b/package/base-files/files/lib/upgrade/tar.sh
>> @@ -0,0 +1,84 @@
> 
> No shebang?

Files /lib/upgrade/*.sh are for including.


>> +# SPDX-License-Identifier: GPL-2.0-or-later OR MIT
>> +
>> +__tar_print_padding() {
>> +    [ $1 -eq 0 ] || dd if=/dev/zero bs=$1 count=1 2>/dev/null
>> +}
>> +
>> +__tar_make_member() {
>> +    local name="$1"
>> +    local content="$2"
>> +    local username="$3"
>> +    local groupname="$4"
>> +    local mtime="$5"
>> +    local mode=644
>> +    local uid=0
>> +    local gid=0
>> +    local size=${#content}
>> +    local type=0
>> +    local link=""
>> +
> 
> recommend that they're ordered here same as struct order:
> 
> struct posix_header
> {                              /* byte offset */
>    char name[100];               /*   0 */
>    char mode[8];                 /* 100 */
>    char uid[8];                  /* 108 */
>    char gid[8];                  /* 116 */
>    char size[12];                /* 124 */
>    char mtime[12];               /* 136 */
>    char chksum[8];               /* 148 */
>    char typeflag;                /* 156 */
>    char linkname[100];           /* 157 */
>    char magic[6];                /* 257 */
>    char version[2];              /* 263 */
>    char uname[32];               /* 265 */
>    char gname[32];               /* 297 */
>    char devmajor[8];             /* 329 */
>    char devminor[8];             /* 337 */
>    char prefix[155];             /* 345 */
>                                  /* 500 */
> };

I'm not sure about it. In the first place I want code to be easy to
understand and maintain. Using some non-natural order (like messing with
order of argument variables and local variables) will be confusing.


>> +    local pad=$'\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1'
>> +
> 
> maybe try:
> 
> local pad=$(printf '\1%.0s' $(seq 100))

They produce the same result I believe:

# echo $'\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1' | md5sum
59c89925a4ef5bee948db1ec5dc9a4c4  -

# echo $(printf '\1%.0s' $(seq 100)) | md5sum
59c89925a4ef5bee948db1ec5dc9a4c4  -

The first is longer however it avoids two subshell executions. I don't
think there's a single winner here.