Changes between Initial Version and Version 1 of VSIPreload

Timestamp:

May 25, 2015, 10:11:47 PM (9 years ago)

Author:

cdestigter

Comment:

--

VSIPreload

@@ +1 @@
+== What is vsipreload? ==
+
+vsipreload is a library included with gdal which can be used to extend [[UserDocs/ReadInZip]] functionality to non-VSI-aware programs.
+
+It works by using the dynamic linker's `LD_PRELOAD` system to override certain libc function calls with GDAL equivalents.
+
+vsipreload currently only works on Linux.
+
+
+== Building vsipreload ==
+
+1. Build GDAL configured with `--with-pic`
+2. 
+{{{
+    g++ -Wl,-soname,libgdal_vsipreload.so.1 -Wall -fPIC port/vsipreload.cpp \
+    -shared -o libgdal_vsipreload.so.1 -Iport -L. -L.libs \
+    -Wl,-Bstatic -lgdal -Wl,-Bdynamic -ldl -lpthread -lcurl
+}}}
+
+Some notes: 
+
+1. statically linked `-lgdal`. This means using `LD_PRELOAD` loads a fairly minimal symbol set, so conflicting symbols with libraries loaded later aren't a problem. Otherwise you may run into problems with conflicting symbols from the various GDAL dependencies. An example is the ESRI FileGDB API, which exports a lot of libxml symbols, and when preloaded it may cause segfaults in other code that uses libxml symbols.
+
+2. (1) requires libgdal to be configured `--with-pic`, otherwise the static linking doesn't work.
+
+3. debhelper/lintian seems to dislike libraries without sonames. You might be able to skip this step; YMMV.
+
+
+== Using vsipreload ==
+
+Just put LD_PRELOAD before your executable, and add the necessary /vsi... path parts to what you're doing:
+
+{{{
+$ LD_PRELOAD="/home/vagrant/host/c/gdal/libgdal_vsipreload.so.1" ls /vsizip/vsicurl/http://svn.osgeo.org/gdal/trunk/autotest/ogr/data/poly.zip
+poly.dbf  poly.PRJ  poly.shp  poly.shx
+}}}