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

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

[Alejandro Colomar]

The glibc wrapper for getdents64() uses ssize_t.
And let's use it also for getdents().
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);
-- 
2.28.0

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

[Michael Kerrisk (man-pages)]

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/

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

[Alejandro Colomar]

[[ CC += linux-kernel, libc-alpha ]]

Hi Michael,

On 2020-10-29 08:13, Michael Kerrisk (man-pages) wrote:
 > 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.

I saw that, but I sent an email to glibc asking if it was a bug.
I'll hold this patch, and I'll CC this list in that other thread.

 >
 >> 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.)

Agreed; then getdents() (and all syscalls without a wrapper)
should use 'long', as you said.

BTW: My mind explodes when I try to read through SYSCALL_DEFINEx :)

 >
 > 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.

Agreed.
I should be able to check if it's needed, in ssize_t(3) :p
... Actually it's not needed (<stdio.h> already provides it).

Thanks,

Alex

[PATCH v2] getdents.2: Use appropriate types

[Alejandro Colomar]

getdents():
This function has no glibc wrapper.
As such, we should use the same types the Linux kernel uses:
Use 'long' as the return type.

getdents64():
The glibc wrapper uses ssize_t for the return type,
and 'size_t' for the count argument.

Signed-off-by: Alejandro Colomar <colomar.6.4.3@gmail.com>
---
 man2/getdents.2 | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/man2/getdents.2 b/man2/getdents.2
index a187fbcef..e14627e6e 100644
--- a/man2/getdents.2
+++ b/man2/getdents.2
@@ -33,14 +33,14 @@
 getdents, getdents64 \- get directory entries
 .SH SYNOPSIS
 .nf
-.BI "int getdents(unsigned int " fd ", struct linux_dirent *" dirp ,
+.BI "long 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 "             unsigned int " count );
+.BI "ssize_t getdents64(unsigned int " fd ", struct linux_dirent64 *" dirp ,
+.BI "             size_t " count );
 .fi
 .PP
 .IR Note :
@@ -282,7 +282,8 @@ struct linux_dirent {
 int
 main(int argc, char *argv[])
 {
-    int fd, nread;
+    int fd;
+    long nread;
     char buf[BUF_SIZE];
     struct linux_dirent *d;
     char d_type;
@@ -301,7 +302,7 @@ 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 (long bpos = 0; bpos < nread;) {
             d = (struct linux_dirent *) (buf + bpos);
             printf("%8ld  ", d\->d_ino);
             d_type = *(buf + bpos + d\->d_reclen \- 1);
-- 
2.28.0

Re: [PATCH v2] getdents.2: Use appropriate types

[Michael Kerrisk (man-pages)]

Hi Alex,

On Thu, 29 Oct 2020 at 14:42, Alejandro Colomar <colomar.6.4.3@gmail.com> wrote:
>
> getdents():
> This function has no glibc wrapper.
> As such, we should use the same types the Linux kernel uses:
> Use 'long' as the return type.
>
> getdents64():
> The glibc wrapper uses ssize_t for the return type,
> and 'size_t' for the count argument.

Take a look in the header file at the argument types for getdents64();
there's still some changes needed.

Thanks,

Michael


> Signed-off-by: Alejandro Colomar <colomar.6.4.3@gmail.com>
> ---
>  man2/getdents.2 | 11 ++++++-----
>  1 file changed, 6 insertions(+), 5 deletions(-)
>
> diff --git a/man2/getdents.2 b/man2/getdents.2
> index a187fbcef..e14627e6e 100644
> --- a/man2/getdents.2
> +++ b/man2/getdents.2
> @@ -33,14 +33,14 @@
>  getdents, getdents64 \- get directory entries
>  .SH SYNOPSIS
>  .nf
> -.BI "int getdents(unsigned int " fd ", struct linux_dirent *" dirp ,
> +.BI "long 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 "             unsigned int " count );
> +.BI "ssize_t getdents64(unsigned int " fd ", struct linux_dirent64 *" dirp ,
> +.BI "             size_t " count );
>  .fi
>  .PP
>  .IR Note :
> @@ -282,7 +282,8 @@ struct linux_dirent {
>  int
>  main(int argc, char *argv[])
>  {
> -    int fd, nread;
> +    int fd;
> +    long nread;
>      char buf[BUF_SIZE];
>      struct linux_dirent *d;
>      char d_type;
> @@ -301,7 +302,7 @@ 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 (long bpos = 0; bpos < nread;) {
>              d = (struct linux_dirent *) (buf + bpos);
>              printf("%8ld  ", d\->d_ino);
>              d_type = *(buf + bpos + d\->d_reclen \- 1);
> --
> 2.28.0
>


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

[PATCH v3] getdents.2: Use appropriate types

[Alejandro Colomar]

getdents():
This function has no glibc wrapper.
As such, we should use the same types the Linux kernel uses:
Use 'long' as the return type.

getdents64():
The glibc wrapper uses:
ssize_t getdents64(int, void *, size_t);

Signed-off-by: Alejandro Colomar <colomar.6.4.3@gmail.com>
---

Hi Michael,

Sorry, I'm being a bit distracted these days :)
It should be good enough now, I think.

Cheers,

Alex

 man2/getdents.2 | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/man2/getdents.2 b/man2/getdents.2
index a187fbcef..ed3bb40b1 100644
--- a/man2/getdents.2
+++ b/man2/getdents.2
@@ -33,14 +33,13 @@
 getdents, getdents64 \- get directory entries
 .SH SYNOPSIS
 .nf
-.BI "int getdents(unsigned int " fd ", struct linux_dirent *" dirp ,
+.BI "long 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 "             unsigned int " count );
+.BI "ssize_t getdents64(int " fd ", void *" dirp ", size_t " count );
 .fi
 .PP
 .IR Note :
@@ -282,7 +281,8 @@ struct linux_dirent {
 int
 main(int argc, char *argv[])
 {
-    int fd, nread;
+    int fd;
+    long nread;
     char buf[BUF_SIZE];
     struct linux_dirent *d;
     char d_type;
@@ -301,7 +301,7 @@ 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 (long bpos = 0; bpos < nread;) {
             d = (struct linux_dirent *) (buf + bpos);
             printf("%8ld  ", d\->d_ino);
             d_type = *(buf + bpos + d\->d_reclen \- 1);
-- 
2.28.0

Re: [PATCH v3] getdents.2: Use appropriate types

[Michael Kerrisk (man-pages)]

On 10/29/20 3:10 PM, Alejandro Colomar wrote:
> getdents():
> This function has no glibc wrapper.
> As such, we should use the same types the Linux kernel uses:
> Use 'long' as the return type.
> 
> getdents64():
> The glibc wrapper uses:
> ssize_t getdents64(int, void *, size_t);
> 
> Signed-off-by: Alejandro Colomar <colomar.6.4.3@gmail.com>

Thanks, Alex. Applied.

Cheers,

Michael


> ---
> 
> Hi Michael,
> 
> Sorry, I'm being a bit distracted these days :)
> It should be good enough now, I think.
> 
> Cheers,
> 
> Alex
> 
>  man2/getdents.2 | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/man2/getdents.2 b/man2/getdents.2
> index a187fbcef..ed3bb40b1 100644
> --- a/man2/getdents.2
> +++ b/man2/getdents.2
> @@ -33,14 +33,13 @@
>  getdents, getdents64 \- get directory entries
>  .SH SYNOPSIS
>  .nf
> -.BI "int getdents(unsigned int " fd ", struct linux_dirent *" dirp ,
> +.BI "long 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 "             unsigned int " count );
> +.BI "ssize_t getdents64(int " fd ", void *" dirp ", size_t " count );
>  .fi
>  .PP
>  .IR Note :
> @@ -282,7 +281,8 @@ struct linux_dirent {
>  int
>  main(int argc, char *argv[])
>  {
> -    int fd, nread;
> +    int fd;
> +    long nread;
>      char buf[BUF_SIZE];
>      struct linux_dirent *d;
>      char d_type;
> @@ -301,7 +301,7 @@ 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 (long 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/