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diff --git a/winsup/doc/faq-api.xml b/winsup/doc/faq-api.xml new file mode 100644 index 000000000..1a9c6c517 --- /dev/null +++ b/winsup/doc/faq-api.xml @@ -0,0 +1,348 @@ +<!-- faq-api.xml --> +<qandaentry id="faq.api.everything"> +<question><para>How does everything work?</para></question> +<answer> + +<para>There's a C library which provides a Unix-style API. The +applications are linked with it and voila - they run on Windows. +</para> +<para>The aim is to add all the goop necessary to make your apps run on +Windows into the C library. Then your apps should run on Unix and +Windows with no changes at the source level. +</para> +<para>The C library is in a DLL, which makes basic applications quite small. +And it allows relatively easy upgrades to the Win32/Unix translation +layer, providing that DLL changes stay backward-compatible. +</para> +<para>For a good overview of Cygwin, you may want to read the paper on Cygwin +published by the Usenix Association in conjunction with the 2d Usenix NT +Symposium in August 1998. It is available in HTML format on the project +WWW site. +</para> +</answer></qandaentry> + +<qandaentry id="faq.api.snapshots"> +<question><para>Are development snapshots for the Cygwin library available?</para></question> +<answer> + +<para>Yes. They're made whenever anything interesting happens inside the +Cygwin library (usually roughly on a nightly basis, depending on how much +is going on). They are only intended for those people who wish to +contribute code to the project. If you aren't going to be happy +debugging problems in a buggy snapshot, avoid these and wait for a real +release. The snapshots are available from +<ulink url="http://cygwin.com/snapshots/">http://cygwin.com/snapshots/</ulink>. +</para> +</answer></qandaentry> + +<qandaentry id="faq.api.cr-lf"> +<question><para>How is the DOS/Unix CR/LF thing handled?</para></question> +<answer> + +<para>Let's start with some background. +</para> +<para>In UNIX, a file is a file and what the file contains is whatever the +program/programmer/user told it to put into it. In Windows, a file is +also a file and what the file contains depends not only on the +program/programmer/user but also the file processing mode. +</para> +<para>When processing in text mode, certain values of data are treated +specially. A \n (new line) written to the file will prepend a \r +(carriage return) so that if you `printf("Hello\n") you in fact get +"Hello\r\n". Upon reading this combination, the \r is removed and the +number of bytes returned by the read is 1 less than was actually read. +This tends to confuse programs dependent on ftell() and fseek(). A +Ctrl-Z encountered while reading a file sets the End Of File flags even +though it truly isn't the end of file. +</para> +<para>One of Cygwin's goals is to make it possible to easily mix Cygwin-ported +Unix programs with generic Windows programs. As a result, Cygwin opens +files in text mode as is normal under Windows. In the accompanying +tools, tools that deal with binaries (e.g. objdump) operate in Unix +binary mode and tools that deal with text files (e.g. bash) operate in +text mode. +</para> +<para>Some people push the notion of globally setting the default processing +mode to binary via mount point options or by setting the CYGWIN +environment variable. But that creates a different problem. In +binary mode, the program receives all of the data in the file, including +a \r. Since the programs will no longer deal with these properly for +you, you would have to remove the \r from the relevant text files, +especially scripts and startup resource files. This is a porter "cop +out", forcing the user to deal with the \r for the porter. +</para> +<para>It is rather easy for the porter to fix the source code by supplying the +appropriate file processing mode switches to the open/fopen functions. +Treat all text files as text and treat all binary files as binary. To be +specific, you can select binary mode by adding <literal>O_BINARY</literal> to +the second argument of an <literal>open</literal> call, or +<literal>"b"</literal> to second argument of an <literal>fopen</literal> call. +You can also call <literal>setmode (fd, O_BINARY)</literal>. +</para> +<para>Note that because the open/fopen switches are defined by ANSI, they +exist under most flavors of Unix; open/fopen will just ignore the switch +since they have no meaning to UNIX. +</para> +<para>Explanation adapted from mailing list email by Earnie Boyd +<earnie_boyd (at) yahoo.com>. +</para> +</answer></qandaentry> + +<qandaentry id="faq.api.threads"> +<question><para>Is the Cygwin library multi-thread-safe?</para></question> +<answer> + +<para>Yes. +</para> +<para>There is also extensive support for 'POSIX threads', see the file +<literal>cygwin.din</literal> for the list of POSIX thread functions provided. +</para> +</answer></qandaentry> + +<qandaentry id="faq.api.winnt"> +<question><para>Why is some functionality only supported in Windows NT?</para></question> +<answer> + +<para>Windows 9x: n. +32 bit extensions and a graphical shell for a 16 bit patch to an +8 bit operating system originally coded for a 4 bit microprocessor, +written by a 2 bit company that can't stand 1 bit of competition. +</para> +<para>But seriously, Windows 9x lacks most of the security-related calls and +has several other deficiencies with respect to its version of the Win32 +API. See the calls.texinfo document for more information as to what +is not supported in Win 9x. +</para> +</answer></qandaentry> + +<qandaentry id="faq.api.fork"> +<question><para>How is fork() implemented?</para></question> +<answer> + +<para>Cygwin fork() essentially works like a non-copy on write version +of fork() (like old Unix versions used to do). Because of this it +can be a little slow. In most cases, you are better off using the +spawn family of calls if possible. +</para> +<para>Here's how it works: +</para> +<para>Parent initializes a space in the Cygwin process table for child. +Parent creates child suspended using Win32 CreateProcess call, giving +the same path it was invoked with itself. Parent calls setjmp to save +its own context and then sets a pointer to this in the Cygwin shared +memory area (shared among all Cygwin tasks). Parent fills in the child's +.data and .bss subsections by copying from its own address space into +the suspended child's address space. Parent then starts the child. +Parent waits on mutex for child to get to safe point. Child starts and +discovers if has been forked and then longjumps using the saved jump +buffer. Child sets mutex parent is waiting on and then blocks on +another mutex waiting for parent to fill in its stack and heap. Parent +notices child is in safe area, copies stack and heap from itself into +child, releases the mutex the child is waiting on and returns from the +fork call. Child wakes from blocking on mutex, recreates any mmapped +areas passed to it via shared area and then returns from fork itself. +</para> +</answer></qandaentry> + +<qandaentry id="faq.api.globbing"> +<question><para>How does wildcarding (globbing) work?</para></question> +<answer> + +<para>If the DLL thinks it was invoked from a DOS style prompt, it runs a +`globber' over the arguments provided on the command line. This means +that if you type <literal>LS *.EXE</literal> from DOS, it will do what you might +expect. +</para> +<para>Beware: globbing uses <literal>malloc</literal>. If your application defines +<literal>malloc</literal>, that will get used. This may do horrible things to you. +</para> +</answer></qandaentry> + +<qandaentry id="faq.api.symlinks"> +<question><para>How do symbolic links work?</para></question> +<answer> + +<para>Cygwin knows of two ways to create symlinks. +</para> +<para>The old method is the only valid one up to but not including version 1.3.0. +If it's enabled (from 1.3.0 on by setting `nowinsymlinks' in the environment +variable CYGWIN) Cygwin generates link files with a magic header. When you +open a file or directory that is a link to somewhere else, it opens the file +or directory listed in the magic header. Because we don't want to have to +open every referenced file to check symlink status, Cygwin marks symlinks +with the system attribute. Files without the system attribute are not +checked. Because remote samba filesystems do not enable the system +attribute by default, symlinks do not work on network drives unless you +explicitly enable this attribute. +</para> +<para>The new method which is introduced with Cygwin version 1.3.0 is enabled +by default or if `winsymlinks' is set in the environment variable CYGWIN. +Using this method, Cygwin generates symlinks by creating Windows shortcuts. +Cygwin created shortcuts have a special header (which is in that way never +created by Explorer) and the R/O attribute set. A DOS path is stored in +the shortcut as usual and the description entry is used to store the POSIX +path. While the POSIX path is stored as is, the DOS path has perhaps to be +rearranged to result in a valid path. This may result in a divergence +between the DOS and the POSIX path when symlinks are moved crossing mount +points. When a user changes the shortcut, this will be detected by Cygwin +and it will only use the DOS path then. While Cygwin shortcuts are shown +without the ".lnk" suffix in `ls' output, non-Cygwin shortcuts are shown +with the suffix. However, both are treated as symlinks. +</para> +<para>Both, the old and the new symlinks can live peacefully together since Cygwin +treats both as symlinks regardless of the setting of `(no)winsymlinks' in +the environment variable CYGWIN. +</para> +</answer></qandaentry> + +<qandaentry id="faq.api.executables"> +<question><para>Why do some files, which are not executables have the 'x' type.</para></question> +<answer> + +<para>When working out the Unix-style attribute bits on a file, the library +has to fill out some information not provided by the WIN32 API. +</para> +<para>It guesses that files ending in .exe and .bat are executable, as are +ones which have a "#!" as their first characters. +</para> +</answer></qandaentry> + +<qandaentry id="faq.api.secure"> +<question><para>How secure is Cygwin in a multi-user environment?</para></question> +<answer> + +<para>As of version 1.5.13, the Cygwin developers are not aware of any feature +in the cygwin dll that would allow users to gain privileges or to access +objects to which they have no rights under Windows. However there is no +guarantee that Cygwin is as secure as the Windows it runs on. Cygwin +processes share some variables and are thus easier targets of denial of +service type of attacks. +</para> +</answer></qandaentry> + +<qandaentry id="faq.api.net-functions"> +<question><para>How do the net-related functions work?</para></question> +<answer> + +<para><emphasis role='bold'>(Please note: This section has not yet been updated for the latest net release.)</emphasis> +</para> +<para>The network support in Cygwin is supposed to provide the Unix API, not +the Winsock API. +</para> +<para>There are differences between the semantics of functions with the same +name under the API. +</para> +<para>E.g., the select system call on Unix can wait on a standard file handles +and handles to sockets. The select call in Winsock can only wait on +sockets. Because of this, cygwin.dll does a lot of nasty stuff behind +the scenes, trying to persuade various Winsock/win32 functions to do what +a Unix select would do. +</para> +<para>If you are porting an application which already uses Winsock, then +using the net support in Cygwin is wrong. +</para> +<para>But you can still use native Winsock, and use Cygwin. The functions +which cygwin.dll exports are called 'cygwin_<name>'. There +are a load of defines which map the standard Unix names to the names +exported by the DLL-- check out include/netdb.h: +</para> +<screen> +..etc.. +void cygwin_setprotoent (int); +void cygwin_setservent (int); +void cygwin_setrpcent (int); +..etc.. +#ifndef __INSIDE_CYGWIN_NET__ +#define endprotoent cygwin_endprotoent +#define endservent cygwin_endservent +#define endrpcent cygwin_endrpcent +..etc.. +</screen> + +<para>The idea is that you'll get the Unix->Cygwin mapping if you include +the standard Unix header files. If you use this, you won't need to +link with libwinsock.a - all the net stuff is inside the DLL. +</para> +<para>The mywinsock.h file is a standard winsock.h which has been hacked to +remove the bits which conflict with the standard Unix API, or are +defined in other headers. E.g., in mywinsock.h, the definition of +struct hostent is removed. This is because on a Unix box, it lives in +netdb. It isn't a good idea to use it in your applications. +</para> +<para>As of the b19 release, this information may be slightly out of date. +</para> +</answer></qandaentry> + +<qandaentry id="faq.api.winsock"> +<question><para>I don't want Unix sockets, how do I use normal Win32 winsock?</para></question> +<answer> + +<para><emphasis role='bold'>(Please note: This section has not yet been updated for the latest net release.)</emphasis> +</para> +<para>To use the vanilla Win32 winsock, you just need to #define Win32_Winsock +and #include "windows.h" at the top of your source file(s). You'll also +want to add -lwsock32 to the compiler's command line so you link against +libwsock32.a. +</para> +</answer></qandaentry> + +<qandaentry id="faq.api.versions"> +<question><para>What version numbers are associated with Cygwin?</para></question> +<answer> + +<para>Cygwin versioning is relatively complicated because of its status as a +shared library. First of all, since October 1998 every Cygwin DLL has +been named <literal>cygwin1.dll</literal> and has a 1 in the release name. +Additionally, there are DLL major and minor numbers that correspond to +the name of the release, and a release number. In other words, +cygwin-1.5.10-2 is <literal>cygwin1.dll</literal>, major version 5, minor version +10, release 2. +</para> +<para>The <literal>cygwin1.dll</literal> major version number gets incremented only when a +change is made that makes existing software incompatible. For example, +the first major version 5 release, cygwin-1.5.0-1, added 64-bit file I/O +operations, which required many libraries to be recompiled and relinked. +The minor version changes every time we make a new backward compatible +Cygwin release available. There is also a <literal>cygwin1.dll</literal> release +version number. The release number is only incremented if we update an +existing release in a way that does not effect the DLL (like a missing +header file). +</para> +<para>There are also Cygwin API major and minor numbers. The major number +tracks important non-backward-compatible interface changes to the API. +An executable linked with an earlier major number will not be compatible +with the latest DLL. The minor number tracks significant API additions +or changes that will not break older executables but may be required by +newly compiled ones. +</para> +<para>Then there is a shared memory region compatibility version number. It is +incremented when incompatible changes are made to the shared memory +region or to any named shared mutexes, semaphores, etc. Finally there +is a mount point registry version number which keeps track +of non-backwards-compatible changes to the registry mount table layout. +This has been <literal>mounts v2</literal> for a long time. For more exciting Cygwin +version number details, check out the <literal>/usr/include/cygwin/version.h</literal> +file. +</para> +</answer></qandaentry> + +<qandaentry id="faq.api.timezone"> +<question><para>Why isn't _timezone set correctly?</para></question> +<answer> + +<para><emphasis role='bold'>(Please note: This section has not yet been updated for the latest net release.)</emphasis> +</para> +<para>Did you explicitly call tzset() before checking the value of _timezone? +If not, you must do so. +</para> +</answer></qandaentry> + +<qandaentry id="faq.api.mouse"> +<question><para>Is there a mouse interface?</para></question> +<answer> + +<para>There is no way to capture mouse events from Cygwin. There are +currently no plans to add support for this. +</para> +</answer></qandaentry> + |