[PATCH 4/4] fs: fat: remove trailing periods from long name

[Heinrich Schuchardt]

Am 2. Februar 2021 00:54:58 MEZ schrieb AKASHI Takahiro <takahiro.akashi at linaro.org>:
>On Mon, Feb 01, 2021 at 01:34:59PM +0100, Heinrich Schuchardt wrote:
>> On 01.02.21 09:18, AKASHI Takahiro wrote:
>> > On Sun, Jan 31, 2021 at 12:09:53AM +0100, Heinrich Schuchardt
>wrote:
>> >> The FAT32 File System Specification [1] requires leading and
>trailing
>> >> spaces as well as trailing periods of long names to be ignored.
>> >>
>> >> This renders a test for '.' and '..' as file name superfluous.
>> >>
>> >> But we must check that the resulting name has at least one
>character.
>> >>
>> >> [1]
>> >>     Microsoft Extensible Firmware Initiative
>> >>     FAT32 File System Specification
>> >>     Version 1.03, December 6, 2000
>> >>     Microsoft Corporation
>> >>     https://www.win.tue.nl/~aeb/linux/fs/fat/fatgen103.pdf
>> >>
>> >> Signed-off-by: Heinrich Schuchardt <xypron.glpk at gmx.de>
>> >> ---
>> >>  fs/fat/fat_write.c | 29 +++++++++++++++++++++++------
>> >>  1 file changed, 23 insertions(+), 6 deletions(-)
>> >>
>> >> diff --git a/fs/fat/fat_write.c b/fs/fat/fat_write.c
>> >> index 0f4786ef0f..1b0a0eda09 100644
>> >> --- a/fs/fat/fat_write.c
>> >> +++ b/fs/fat/fat_write.c
>> >> @@ -1237,12 +1237,32 @@ again:
>> >>  		}
>> >>
>> >>  		*last_slash_cont = '\0';
>> >> -		*basename = last_slash_cont + 1;
>> >> +		filename = last_slash_cont + 1;
>> >>  	} else {
>> >>  		*dirname = "/"; /* root by default */
>> >> -		*basename = filename;
>> >>  	}
>> >>
>> >> +	/*
>> >> +	 * The FAT32 File System Specification v1.03 requires leading
>and
>> >> +	 * trailing spaces as well as trailing periods to be ignored.
>> >> +	 */
>> >> +	for (; *filename == ' '; ++filename)
>> >> +		;
>> >> +	/* Remove trailing periods and spaces */
>> >> +	for (p = filename + strlen(filename) - 1; p >= filename; --p) {
>> >> +		switch (*p) {
>> >> +		case ' ':
>> >> +		case '.':
>> >> +			*p = 0;
>> >> +			break;
>> >> +		default:
>> >> +			goto done;
>> >> +		}
>> >> +	}
>> >
>> > Given the semantics of the functions, split_filename() and
>normalize_longname(),
>> > the code you added above should be moved to normalize_longname().
>> 
>> normalize_longname(l_filename, filename) converts the argument
>filename
>> to a lowercase string l_filename. The parameter filename remains
>> unchanged. But it is the value of filename that is used to create the
>> new directory entry in file_fat_write_at() and fat_mkdir().
>
>That is why I also suggested, "I even think it would be best to move it
>to
>the caller, file_fat_write_at() or fat_mkdir()."
>
>> So moving the change to normalize_longname() will not lead to the
>> intended behavior.
>> 
>> Removing leading and trailing blanks fits well into the task of
>> split_filename to identify the actual file name.
>
>Again, "." and ".." are legal directory names.
>To reject a request of creating such names is a caller's job,
>not split_filename()'s as its name suggests.
>

These filenames are illegal for all callers.

We should not duplicate code in each caller.

Best regards

Heinrich


>-Takahiro Akashi
>
>> Best regards
>> 
>> Heinrich
>> 
>> >
>> >> +done:
>> >> +	*basename = filename;
>> >> +
>> >>  	return 0;
>> >>  }
>> >>
>> >> @@ -1260,10 +1280,7 @@ static int normalize_longname(char
>*l_filename, const char *filename)
>> >>  {
>> >>  	const char *p, illegal[] = "<>:\"/\\|?*";
>> >>
>> >> -	if (!strcmp(filename, ".") || !strcmp(filename, ".."))
>> >> -		return -1;
>> >
>> > It would be better for the check above to remain here as "." and
>".." are
>> > legal directory names. (I even think it would be best to move it to
>> > the caller, file_fat_write_at() or fat_mkdir().)
>> >
>> > I think that the suggested sequence would be more intuitive for
>> > better understanding of what Windows requirements say.
>> >
>> > -Takahiro Akashi
>> >
>> >> -	if (strlen(filename) >= VFAT_MAXLEN_BYTES)
>> >> +	if (!*filename || strlen(filename) >= VFAT_MAXLEN_BYTES)
>> >>  		return -1;
>> >>
>> >>  	for (p = filename; *p; ++p) {
>> >> --
>> >> 2.29.2
>> >>
>>