Re: [PATCH] getdents.2: Use 'ssize_t' instead of 'int'

Michael Kerrisk (man-pages)
2020-10-29T07:23:04Z

Hi Alex,

On 10/28/20 11:11 PM, Alejandro Colomar wrote:
> The glibc wrapper for getdents64() uses ssize_t.

It also changed the types for the arguments, so those need to be
fixed too.

> And let's use it also for getdents().

I actually think we should *not* change that. So long as their is
no wrapper, we should show pretty much what the ABI exposes. (That
makes me think that the return type should really be long; see
what you think about DEFINE_SYSCALL3 in the kernel sources.)

And you added an include for <sys/types.h>. I'm not sure
whether that's needed, but it should be explained in the
commit message.

Thanks,

Michael

> It makes more sense than int:
> It's a count of bytes, and can report an error (-1).
>
> Signed-off-by: Alejandro Colomar <colomar.6.4.3@gmail.com>
> ---
> man2/getdents.2 | 10 ++++++----
> 1 file changed, 6 insertions(+), 4 deletions(-)
>
> diff --git a/man2/getdents.2 b/man2/getdents.2
> index a187fbcef..d660f1bc1 100644
> --- a/man2/getdents.2
> +++ b/man2/getdents.2
> @@ -33,13 +33,13 @@
> getdents, getdents64 \- get directory entries
> .SH SYNOPSIS
> .nf
> -.BI "int getdents(unsigned int " fd ", struct linux_dirent *" dirp ,
> +.BI "ssize_t getdents(unsigned int " fd ", struct linux_dirent *" dirp ,
> .BI " unsigned int " count );
> .PP
> .BR "#define _GNU_SOURCE" " /* See feature_test_macros(7) */"
> .B #include <dirent.h>
> .PP
> -.BI "int getdents64(unsigned int " fd ", struct linux_dirent64 *" dirp ,
> +.BI "ssize_t getdents64(unsigned int " fd ", struct linux_dirent64 *" dirp ,
> .BI " unsigned int " count );
> .fi
> .PP
> @@ -266,6 +266,7 @@ inode# file type d_reclen d_off d_name
> #include <stdlib.h>
> #include <sys/stat.h>
> #include <sys/syscall.h>
> +#include <sys/types.h>
>
> #define handle_error(msg) \e
> do { perror(msg); exit(EXIT_FAILURE); } while (0)
> @@ -282,7 +283,8 @@ struct linux_dirent {
> int
> main(int argc, char *argv[])
> {
> - int fd, nread;
> + int fd;
> + ssize_t nread;
> char buf[BUF_SIZE];
> struct linux_dirent *d;
> char d_type;
> @@ -301,7 +303,7 @@ main(int argc, char *argv[])
>
> printf("\-\-\-\-\-\-\-\-\-\-\-\-\-\-\- nread=%d \-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\en", nread);
> printf("inode# file type d_reclen d_off d_name\en");
> - for (int bpos = 0; bpos < nread;) {
> + for (ssize_t bpos = 0; bpos < nread;) {
> d = (struct linux_dirent *) (buf + bpos);
> printf("%8ld ", d\->d_ino);
> d_type = *(buf + bpos + d\->d_reclen \- 1);
>

--
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/