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[[!meta copyright="Copyright © 2012, 2013 Free Software Foundation, Inc."]]
[[!meta license="""[[!toggle id="license" text="GFDL 1.2+"]][[!toggleable
id="license" text="Permission is granted to copy, distribute and/or modify this
document under the terms of the GNU Free Documentation License, Version 1.2 or
any later version published by the Free Software Foundation; with no Invariant
Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license
is included in the section entitled [[GNU Free Documentation
License|/fdl]]."]]"""]]
Porting Guide for Dummies
=========================
The problems addressed here were encountered while working
on fixing **PATH_MAX** and **MAXPATHLEN**.
[[!toc startlevel=2 levels=3]]
* * *
Test on Hurd
------------
### Installing the required files
As `apt source` will download and extract many files, you may want to create a dedicated folder for the package and work from there.
mkdir PACKAGE
cd PACKAGE
sudo apt build-dep PACKAGE
apt source PACKAGE
### Trying to build the package
cd PACKAGE_SOURCE
dpkg-buildpackage -us -uc -rfakeroot -tc
### Test a quick fix
In all the files that use **PATH_MAX**, include those lines at the beginning.
#ifndef PATH_MAX
#define PATH_MAX 4196
#endif
Try to rebuild the package and see if it's solved the problem.
If yes, you can start working on the package.
* * *
Basic things
------------
### Maintaining a original version
mkdir old
cp -r PACKAGE_SOURCE old/
### Coding style
Follow the conventions used in the source code!
if (condition) {
do_smthg();
}
is not the same as:
if (condition)
{
do_smthg();
}
and is not the same as:
if (condition)
do_smthg();
Pay attention to spaces surrounding, or not, arithmetic signs and symbols:
a = do_smthg( b + c );
a = do_smthg(b+c);
### Indentation
By default use 8 spaces as the size for 1 tab.
Then figure out if the code uses tab + 1/2 tab:
....if (condition) {
------->do_smthg();
....}
or tab only:
------->if (condition) {
------->------->do_smthg();
------->}
### Creating a patch
diff -Naur old/PACKAGE-VERSION PACKAGE-VERSION > fix_FTBFS4Hurd.patch
* * *
Known problems
--------------
### Dynamically allocated buffer returned by a function
Use a static buffer
### Buffer used to format an expression containing an INTEGER
The length of an INTEGER in a string can be up to sizeof (int) * 3 + 1.
> The usual trick for "%d" is to use the constant 'sizeof (int) * 3 + 1'.
I included + 1 for the sign, but it's not really necessary
if we exepect sizeof(int) >= 2, which we probably should.
**Jérémie Koenig**
log(MAX_INT)
= log(2 ^ 32)
= 32 * log(2)
= 4 * 8 * log(2)
= sizeof(int) * 2.40823997
< sizeof(int) * 3
### Proper use of realloc()
use a new_buff to check if everything went fine Free buf if realloc failed (and prog doesn't exit)
### Reading lines from file
Function to read line (no size limit, ending with "\n") from a file.
static char *get_line(FILE *f)
{
char *buff = NULL;
char *new_buff = NULL;
size_t buff_size = 0;
size_t last = 0;
while (!feof(f)) {
buff_size = buff_size ? buff_size * 2 : BUFSIZ;
new_buff = realloc(buff, buff_size);
if (new_buff == NULL) {
free(buff);
return NULL;
}
buff = new_buff;
if (fgets(buff + last, buff_size - last, f) == NULL) {
free(buff);
return NULL;
}
last = strlen(buff);
if (buff[last - 1] == '\n')
return buff;
}
return buff;
}
### Proper use of readlink()
One has to rely on lstat() to get the size of the link that readlink() returns.
Declare what you need:
char *linkname = NULL;
struct stat sb;
ssize_t len = -1;
Call lstat() and check return value:
if (lstat(filename, &sb) == -1) {
Create a buffer of the appropriate size and check the return value:
linkname = malloc(sb.st_size + 1);
if (linkname == NULL) {
Call readlink(), check return value and set the null char in the linkname:
len = readlink(filename, linkname, sb.st_size + 1);
if (len < 0 || len > sb.st_size) {
...
linkname[len] = '\0';
### Alternative use of readlink(): readlink_malloc()
In some cases the above approch doesn't work.for instance when reading from
**/proc/*/exe** on Linux. In this case you can try the following function.
The code comes from [[https://buildsecurityin.us-cert.gov/bsi/articles/knowledge/coding/806-BSI.html]]
static char *readlink_malloc(const char *filename)
{
int size = 100;
while (1) {
char *buff = malloc(size);
if (buff == NULL)
return NULL;
int nchars = readlink(filename, buff, size);
if (nchars < 0) {
free(buff);
return NULL;
}
if (nchars < size) {
buff[nchars] = '\0';
return buff;
}
free (buff);
size *= 2;
}
}
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