On Sun, Jun 29, 2014 at 11:57 AM, Renji Panicker <renjipanic...@gmail.com> wrote:
> I am developing a shim, and am facing a problem (or it might be a defect in > the sample shims I have seen so far): > (1) test_vfstrace.c is probably a better example of a shim than test_multiplex.c, at least for use as a basis for some new shim. The subclass of sqlite3_file used by test_vfstrace.c is defined here: http://www.sqlite.org/src/artifact/bab9594adc?ln=130-136 If some variable "p" is a pointer to the vfstrace object, then the underlying sqlite3_file object immediately follows it in memory. In other words, the underlying sqlite3_file is at (sqlite3_file*)p[1]. > > - When I receive a call to my xOpen function, the 3rd parameter is a > sqlite3_file* type. > > - As per the sqlite3PagerOpen function, the size of the memory allocated to > this pointer is ROUND8(pVfs->szOsFile). > > - On Windows, the value of szOsFile is sizeof(winFile) + sizeof(myFile). > > - As per the sample shims, in my xOpen handler, I must typecast the > sqlite3_file* value to myFile* > > Does this mean that winFile and myFile are now overlapping at the same > memory location? > > For example: if sqlite3_file is defined as: > > struct sqlite3_file { > > const struct sqlite3_io_methods *pMethods; /* Methods for an open file */ > > }; > and winFile is defined as: > > struct winFile { > > const sqlite3_io_methods *pMethod; /*** Must be first ***/ > > sqlite3_vfs *pVfs; /* The VFS used to open this file */ > > }; > > and myFile is defined as (taken from multiplex sample shim): > > struct myFile { > sqlite3_file base; /* Base class - must be first */ > multiplexGroup *pGroup; /* The underlying group of files */ > > }; > > Wouldn't winFile::pVfs and myFile::pGroup be at the same location in > memory? > _______________________________________________ > sqlite-users mailing list > sqlite-users@sqlite.org > http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users > -- D. Richard Hipp d...@sqlite.org _______________________________________________ sqlite-users mailing list sqlite-users@sqlite.org http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
