dry-75 commented on code in PR #2456:
URL: https://github.com/apache/nuttx-apps/pull/2456#discussion_r1699920300
##########
nshlib/nsh_ddcmd.c:
##########
@@ -385,7 +385,7 @@ int cmd_dd(FAR struct nsh_vtbl_s *vtbl, int argc, FAR char
**argv)
if (dd.skip)
{
ret = lseek(dd.infd, dd.skip * dd.sectsize, SEEK_SET);
- if (ret < -1)
+ if (ret < 0)
Review Comment:
What Yamamoto seems to assert ( but he didn't specifically linked to it) is
that in the old if not outdated POSIX - see under Rationale in your link
provided @xiaoxiang781216
"...The POSIX.1-1990 standard did not specifically prohibit lseek() from
returning a negative offset..." etc.
In same URL, and all way to updated POSIX 2024 page of lseek, that
Rationalte section is under header / page section titled "_The following
sections are informative_". One way to read that is, Information FYI nice to
know history.
But at the same time, the return value para does not still explicitly state
that the offset from beginning of the file cannot be negative.
> RETURN VALUE
Upon successful completion, the resulting offset, as measured in bytes from
the beginning of the file, shall be returned. Otherwise, -1 shall be returned,
errno shall be set to indicate the error, and the file offset shall remain
unchanged.
To which POSIX whole of NuttX conforms I do not know, and if this special
case if of any use in current base. My guess is if this suggested change would
work for most cases and only breaks when using some files which return negative
other than -1 to signal error , well they are broken.
I can submit this change, otherwise if anyone is interested to dig more into
this I would have to pass as I would like to focus on other things.
I found the comment/discussion informative however, as I always used lseek
with closed eyes wrt. to the possibility of it returning a negative while not
in error. (But then again, all use cases I recall using it, It would never
make sense for it to return a valid negative value which would not signal and
error, whatever it would be actually).
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