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diff --git a/user/tlecarrour/porting_guide_for_dummies.mdwn b/user/tlecarrour/porting_guide_for_dummies.mdwn new file mode 100644 index 00000000..64f0ba0d --- /dev/null +++ b/user/tlecarrour/porting_guide_for_dummies.mdwn @@ -0,0 +1,230 @@ +[[!meta copyright="Copyright © 2012 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-get 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-get build-dep PACKAGE + apt-get 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[sb.st_size] = '\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) + return NULL; + if (nchars < size) { + buff[nchars] = '\0'; + return buff; + } + free (buff); + size *= 2; + } + } + |