Building and Installing Software Packages for Linux: Third Example: Fortune

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## 11. Third Example: Fortune

This example requires some knowledge of C programming. The majority of UNIX/Linux software is written in C, and learning at least a little bit of C would certainly be an asset for anyone serious about software installation.

The notorious fortune program displays up a humorous saying, a "fortune cookie", every time Linux boots up. Unfortunately (pun intended), attempting to build fortune on a Red Hat distribution with a 2.0.30 kernel generates fatal errors.

> `

>     ~/fortune# make all

>     gcc -O2 -Wall -fomit-frame-pointer -pipe   -c fortune.c -o
>     fortune.o
>     fortune.c: In function `add_dir':
>     fortune.c:551: structure has no member named `d_namlen'
>     fortune.c:553: structure has no member named `d_namlen'
>     make[1]: *** [fortune.o] Error 1
>     make[1]: Leaving directory `/home/thegrendel/for/fortune/fortune'
>     make: *** [fortune-bin] Error 2

> `

Looking at `fortune.c`, the pertinent lines are these.

> `

>        if (dirent->d_namlen == 0)
>                 continue;
>             name = copy(dirent->d_name, dirent->d_namlen);

> `

We need to find the structure `dirent`, but it is not declared in the fortune.c file, nor does a grep dirent show it in any of the other source files. However, at the top of fortune.c, there is the following line.

> `

>     #include <dirent.h>

> `

This appears to be a system library include file, therefore, the logical place to look for dirent.h is in /usr/include. Indeed, there does exist a dirent.h file in /usr/include, but that file does not contain the declaration of the `dirent` structure. There is, however, a reference to another dirent.h file.

> `

>     #include <linux/dirent.h>

> `

At last, going to /usr/include/linux/dirent.h, we find the structure declaration we need.

> `

>     struct dirent {
>             long            d_ino;
>             __kernel_off_t  d_off;
>             unsigned short  d_reclen;
>             char            d_name[256]; /* We must not include
>     limits.h! */
>     };

> `

Sure enough, the structure declaration contains no d_namelen, but there are a couple of "candidates" for its equivalent. The most likely of these is d_reclen, since this structure member probably represents the length of something and it is a short integer. The other possibility, d_ino, could be an inode number, judging by its name and type. As a matter of fact, we are probably dealing with a "directory entry" structure, and these elements represent attributes of a file, its name, inode, and length (in blocks). This would seem to validate our guess.

Let us edit the file `fortune.c`, and change the two d_namelen references in lines 551 and 553 to d_reclen. Try a make all again. Success. It builds without errors. We can now get our "cheap thrills" from fortune.

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