X-Git-Url: http://git.annexia.org/?a=blobdiff_plain;ds=sidebyside;f=guestfs.pod;h=fb16f572227af82f619cab2e877ae027bb9c9da0;hb=62d6ae454f1f75b2a8dc29e681586db73884cd08;hp=3aa806abd9c2c8c77edd9562da377f2d6ff4e5c3;hpb=5f9be62e68b120f51c948404e7f0cf3430962c68;p=libguestfs.git

diff --git a/guestfs.pod b/guestfs.pod
index 3aa806a..fb16f57 100644
--- a/guestfs.pod
+++ b/guestfs.pod
@@ -105,8 +105,8 @@ return error indications.
 =head2 DISK IMAGES
 
 The image filename (C<"guest.img"> in the example above) could be a
-disk image from a virtual machine, a L<dd(1)> copy of a physical block
-device, an actual block device, or simply an empty file of zeroes that
+disk image from a virtual machine, a L<dd(1)> copy of a physical hard
+disk, an actual block device, or simply an empty file of zeroes that
 you have created through L<posix_fallocate(3)>.  Libguestfs lets you
 do useful things to all of these.
 
@@ -142,7 +142,7 @@ first disk image that we added (C</dev/sda>).  If the disk contains
 Linux LVM2 logical volumes you could refer to those instead (eg. C</dev/VG/LV>).
 
 If you are given a disk image and you don't know what it contains then
-you have to find out.  Libguestfs can also do that: use
+you have to find out.  Libguestfs can do that too: use
 C<guestfs_list_partitions> and C<guestfs_lvs> to list possible
 partitions and LVs, and either try mounting each to see what is
 mountable, or else examine them with C<guestfs_file>.  But you might
@@ -274,6 +274,41 @@ non-portable between kernel versions, and they don't support labels or
 UUIDs.  If you want to pre-build an image or you need to mount it
 using a label or UUID, use an ISO image instead.
 
+=head2 COPYING
+
+There are various different commands for copying between files and
+devices and in and out of the guest filesystem.  These are summarised
+in the table below.
+
+=over 4
+
+=item B<file> to B<file>
+
+Use L</guestfs_cp> to copy a single file, or
+L</guestfs_cp_a> to copy directories recursively.
+
+=item B<file or device> to B<file or device>
+
+Use L</guestfs_dd> which efficiently uses L<dd(1)>
+to copy between files and devices in the guest.
+
+Example: duplicate the contents of an LV:
+
+ guestfs_dd (g, "/dev/VG/Original", "/dev/VG/Copy");
+
+The destination (C</dev/VG/Copy>) must be at least as large as the
+source (C</dev/VG/Original>).
+
+=item B<file on the host> to B<file or device>
+
+Use L</guestfs_upload>.  See L</UPLOADING> above.
+
+=item B<file or device> to B<file on the host>
+
+Use L</guestfs_download>.  See L</DOWNLOADING> above.
+
+=back
+
 =head2 LISTING FILES
 
 C<guestfs_ll> is just designed for humans to read (mainly when using
@@ -424,16 +459,26 @@ help on this issue.
 Although we don't want to discourage you from using the C API, we will
 mention here that the same API is also available in other languages.
 
-The API is broadly identical in all supported languages.  As an
-example, in Python the handle itself is replaced by an object, but we
-don't try to "object orientify" any other parts of the API.
+The API is broadly identical in all supported languages.  This means
+that the C call C<guestfs_mount(handle,path)> is
+C<$handle-E<gt>mount($path)> in Perl, C<handle.mount(path)> in Python,
+and C<Guestfs.mount handle path> in OCaml.  In other words, a
+straightforward, predictable isomorphism between each language.
+
+Error messages are automatically transformed
+into exceptions if the language supports it.
+
+We don't try to "object orientify" parts of the API in OO languages,
+although contributors are welcome to write higher level APIs above
+what we provide in their favourite languages if they wish.
 
 =over 4
 
 =item B<C++>
 
 You can use the I<guestfs.h> header file from C++ programs.  The C++
-API is identical to the C API.
+API is identical to the C API.  C++ classes and exceptions are
+not implemented.
 
 =item B<Haskell>
 
@@ -613,6 +658,86 @@ developer to program in confidence against libguestfs.
 
 @STRUCTS@
 
+=head1 AVAILABILITY
+
+=head2 GROUPS OF FUNCTIONALITY IN THE APPLIANCE
+
+Using L</guestfs_available> you can test availability of
+the following groups of functions.  This test queries the
+appliance to see if the appliance you are currently using
+supports the functionality.
+
+@AVAILABILITY@
+
+=head2 SINGLE CALLS AT COMPILE TIME
+
+If you need to test whether a single libguestfs function is
+available at compile time, we recommend using build tools
+such as autoconf or cmake.  For example in autotools you could
+use:
+
+ AC_CHECK_LIB([guestfs],[guestfs_create])
+ AC_CHECK_FUNCS([guestfs_dd])
+
+which would result in C<HAVE_GUESTFS_DD> being either defined
+or not defined in your program.
+
+=head2 SINGLE CALLS AT RUN TIME
+
+Testing at compile time doesn't guarantee that a function really
+exists in the library.  The reason is that you might be dynamically
+linked against a previous I<libguestfs.so> (dynamic library)
+which doesn't have the call.  This situation unfortunately results
+in a segmentation fault, which is a shortcoming of the C dynamic
+linking system itself.
+
+You can use L<dlopen(3)> to test if a function is available
+at run time, as in this example program (note that you still
+need the compile time check as well):
+
+ #include <config.h>
+ 
+ #include <stdio.h>
+ #include <stdlib.h>
+ #include <unistd.h>
+ #include <dlfcn.h>
+ #include <guestfs.h>
+ 
+ main ()
+ {
+ #ifdef HAVE_GUESTFS_DD
+   void *dl;
+   int has_function;
+
+   /* Test if the function guestfs_dd is really available. */
+   dl = dlopen (NULL, RTLD_LAZY);
+   if (!dl) {
+     fprintf (stderr, "dlopen: %s\n", dlerror ());
+     exit (1);
+   }
+   has_function = dlsym (dl, "guestfs_dd") != NULL;
+   dlclose (dl);
+ 
+   if (!has_function)
+     printf ("this libguestfs.so does NOT have guestfs_dd function\n");
+   else {
+     printf ("this libguestfs.so has guestfs_dd function\n");
+     /* Now it's safe to call
+     guestfs_dd (g, "foo", "bar");
+     */
+   }
+ #else
+   printf ("guestfs_dd function was not found at compile time\n");
+ #endif
+  }
+
+You may think the above is an awful lot of hassle, and it is.
+There are other ways outside of the C linking system to ensure
+that this kind of incompatibility never arises, such as using
+package versioning:
+
+ Requires: libguestfs >= 1.0.80
+
 =head1 STATE MACHINE AND LOW-LEVEL EVENT API
 
 Internally, libguestfs is implemented by running a virtual machine