[5/8] malloc/{memusage.c, memusagestat.c}: fix warn unused result

Fix unused result warnings, detected when _FORTIFY_SOURCE is enabled in
glibc.
---
 malloc/memusage.c     | 38 ++++++++++++++++++++++++++------------
 malloc/memusagestat.c | 13 +++++++++----
 2 files changed, 35 insertions(+), 16 deletions(-)

On 2023-04-18 08:11, Frédéric Bérat via Libc-alpha wrote:
> Fix unused result warnings, detected when _FORTIFY_SOURCE is enabled in
> glibc.
> ---
>   malloc/memusage.c     | 38 ++++++++++++++++++++++++++------------
>   malloc/memusagestat.c | 13 +++++++++----
>   2 files changed, 35 insertions(+), 16 deletions(-)
> 
> diff --git a/malloc/memusage.c b/malloc/memusage.c
> index 2a3a508557..6251e039b0 100644
> --- a/malloc/memusage.c
> +++ b/malloc/memusage.c
> @@ -18,6 +18,8 @@
>   
>   #include <assert.h>
>   #include <dlfcn.h>
> +#include <errno.h>
> +#include <error.h>
>   #include <fcntl.h>
>   #include <stdatomic.h>
>   #include <stdbool.h>
> @@ -210,10 +212,12 @@ update_data (struct header *result, size_t len, size_t old_len)
>         gettime (&buffer[idx]);
>   
>         /* Write out buffer if it is full.  */
> -      if (idx + 1 == buffer_size)
> -        write (fd, buffer, buffer_size * sizeof (struct entry));
> -      else if (idx + 1 == 2 * buffer_size)
> -        write (fd, &buffer[buffer_size], buffer_size * sizeof (struct entry));
> +      if (idx + 1 == buffer_size || idx + 1 == 2 * buffer_size)
> +        {
> +          uint32_t write_size = buffer_size * sizeof (buffer[0]);
> +          if (write (fd, &buffer[idx + 1 - buffer_size], write_size) < write_size)
> +              error(EXIT_FAILURE, errno, "cannot write buffer");

Same as patch 2/8, maybe it makes sense to make a higher level 
abstraction for read and write to ensure all contents are read/written.

Thanks,
Sid

> +        }
>       }
>   }
>   
> @@ -299,8 +303,10 @@ me (void)
>                 first.stack = 0;
>                 gettime (&first);
>                 /* Write it two times since we need the starting and end time. */
> -              write (fd, &first, sizeof (first));
> -              write (fd, &first, sizeof (first));
> +              if (write (fd, &first, sizeof (first)) < sizeof (first))
> +                error(EXIT_FAILURE, errno, "cannot write entry");
> +              if (write (fd, &first, sizeof (first)) < sizeof (first))
> +                error(EXIT_FAILURE, errno, "cannot write entry");
>   
>                 /* Determine the buffer size.  We use the default if the
>                    environment variable is not present.  */
> @@ -850,24 +856,32 @@ dest (void)
>     if (fd != -1)
>       {
>         /* Write the partially filled buffer.  */
> +      struct entry *start = buffer;
> +      uint32_t write_cnt = buffer_cnt;
> +
>         if (buffer_cnt > buffer_size)
> -        write (fd, buffer + buffer_size,
> -               (buffer_cnt - buffer_size) * sizeof (struct entry));
> -      else
> -        write (fd, buffer, buffer_cnt * sizeof (struct entry));
> +        {
> +          start = buffer + buffer_size;
> +          write_cnt = buffer_cnt - buffer_size;
> +        }
> +
> +      if (write(fd, start, write_cnt * sizeof (buffer[0])) < sizeof (buffer[0]))
> +        error(EXIT_FAILURE, errno, "cannot write buffer");
>   
>         /* Go back to the beginning of the file.  We allocated two records
>            here when we opened the file.  */
>         lseek (fd, 0, SEEK_SET);
>         /* Write out a record containing the total size.  */
>         first.stack = peak_total;
> -      write (fd, &first, sizeof (struct entry));
> +      if (write (fd, &first, sizeof (first)) < sizeof (first))
> +        error(EXIT_FAILURE, errno, "cannot write first");
>         /* Write out another record containing the maximum for heap and
>            stack.  */
>         first.heap = peak_heap;
>         first.stack = peak_stack;
>         gettime (&first);
> -      write (fd, &first, sizeof (struct entry));
> +      if (write (fd, &first, sizeof (first)) < sizeof (first))
> +        error(EXIT_FAILURE, errno, "cannot write first");
>   
>         /* Close the file.  */
>         close (fd);
> diff --git a/malloc/memusagestat.c b/malloc/memusagestat.c
> index 67c5131f79..3853f00b9b 100644
> --- a/malloc/memusagestat.c
> +++ b/malloc/memusagestat.c
> @@ -188,7 +188,8 @@ main (int argc, char *argv[])
>     total = st.st_size / sizeof (struct entry) - 2;
>   
>     /* Read the administrative information.  */
> -  read (fd, headent, sizeof (headent));
> +  if (read (fd, headent, sizeof (headent)) < sizeof (headent))
> +    error(EXIT_FAILURE, errno, "cannot read entry header");
>     maxsize_heap = headent[1].heap;
>     maxsize_stack = headent[1].stack;
>     maxsize_total = headent[0].stack;
> @@ -220,7 +221,9 @@ main (int argc, char *argv[])
>   
>         /* Write the computed values in the file.  */
>         lseek (fd, 0, SEEK_SET);
> -      write (fd, headent, 2 * sizeof (struct entry));
> +      if (write (fd, headent, sizeof (headent)) < sizeof (headent))
> +        error(EXIT_FAILURE, errno, "cannot write entries");
> +
>       }
>   
>     if (also_total)
> @@ -372,7 +375,8 @@ main (int argc, char *argv[])
>             size_t new[2];
>             uint64_t now;
>   
> -          read (fd, &entry, sizeof (entry));
> +          if (read (fd, &entry, sizeof (entry)) < sizeof (entry))
> +            error(EXIT_FAILURE, errno, "cannot read entry");
>   
>             now = ((uint64_t) entry.time_high) << 32 | entry.time_low;
>   
> @@ -455,7 +459,8 @@ main (int argc, char *argv[])
>             size_t xpos;
>             uint64_t now;
>   
> -          read (fd, &entry, sizeof (entry));
> +          if (read (fd, &entry, sizeof (entry)) < sizeof (entry))
> +            error(EXIT_FAILURE, errno, "cannot read entry");
>   
>             now = ((uint64_t) entry.time_high) << 32 | entry.time_low;
>             xpos = 40 + ((xsize - 80) * (now - start_time)) / total_time;