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

[AKASHI Takahiro]

On Tue, Feb 02, 2021 at 07:05:53AM +0100, Heinrich Schuchardt wrote:
> 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.

The purpose of split_filename() is to separate a file name from
its directory path. As I said, excluding "." or ".." is out of this
function's scope, but the caller's semantics.

> We should not duplicate code in each caller.

I don't think so.
handling "." or ".." entry and removing leading/trailing spaces
are totally different.

-Takahiro Akashi

> 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
> >> >>
> >> 
>