Thread: incompatible pointer types with newer zlib
According to me update logs, somewhere between zlib versions 1.2.3.4 and 1.2.6, the definition of the gzFile type was changed from void * to struct gzFile_s *, an opaque struct. Note that gzFile is already the pointer in either case. Our code has assumed, however, that you use gzFile like FILE, namely that the APIs take a pointer to the type, but that is not the case. So code like gzFile *handle = gzopen(...) is wrong. This used to pass silently because you can assign a void* to a void**, but with the newer definition you get a bunch of warnings like pg_backup_files.c: In function ‘_StartData’: pg_backup_files.c:256:11: warning: assignment from incompatible pointer type [enabled by default] pg_backup_files.c: In function ‘_WriteData’: pg_backup_files.c:271:2: warning: passing argument 1 of ‘gzwrite’ from incompatible pointer type [enabled by default] /usr/include/zlib.h:1318:12: note: expected ‘gzFile’ but argument is of type ‘struct gzFile_s **’ Affected are pg_dump and pg_basebackup. Fixing most of this is not difficult, see attached patch. The only ugliness is in pg_backup_archiver.h FILE *FH; /* General purpose file handle */ which is used throughout pg_dump as sometimes a real FILE* and sometimes a gzFile handle. There are also some fileno() calls on this, so just replacing this with an #ifdef isn't going to work. This might need some more restructuring to make the code truly type-safe. My quick patch replaces the type with void*, thus sort of restoring the original situation that allowed this to work. Note that these are only warnings, so we probably don't need to worry about backpatching this in a hurry.
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Peter Eisentraut <peter_e@gmx.net> writes:
> Fixing most of this is not difficult, see attached patch. The only
> ugliness is in pg_backup_archiver.h
> FILE *FH; /* General purpose file handle */
> which is used throughout pg_dump as sometimes a real FILE* and sometimes
> a gzFile handle. There are also some fileno() calls on this, so just
> replacing this with an #ifdef isn't going to work. This might need some
> more restructuring to make the code truly type-safe. My quick patch
> replaces the type with void*, thus sort of restoring the original
> situation that allowed this to work.
void * seems entirely reasonable given the two different usages, but
I would be happier if the patch added explicit casts whereever FH is
set to or used as one of these two types.
regards, tom lane
On tor, 2012-02-23 at 10:17 -0500, Tom Lane wrote: > Peter Eisentraut <peter_e@gmx.net> writes: > > Fixing most of this is not difficult, see attached patch. The only > > ugliness is in pg_backup_archiver.h > > > FILE *FH; /* General purpose file handle */ > > > which is used throughout pg_dump as sometimes a real FILE* and sometimes > > a gzFile handle. There are also some fileno() calls on this, so just > > replacing this with an #ifdef isn't going to work. This might need some > > more restructuring to make the code truly type-safe. My quick patch > > replaces the type with void*, thus sort of restoring the original > > situation that allowed this to work. > > void * seems entirely reasonable given the two different usages, but > I would be happier if the patch added explicit casts whereever FH is > set to or used as one of these two types. That would add about 70 casts all over the place. I don't think that will make things clearer or more robust. I think we either leave it as my first patch for now or find a more robust solution with a union or something.
Peter Eisentraut <peter_e@gmx.net> writes:
> On tor, 2012-02-23 at 10:17 -0500, Tom Lane wrote:
>> void * seems entirely reasonable given the two different usages, but
>> I would be happier if the patch added explicit casts whereever FH is
>> set to or used as one of these two types.
> That would add about 70 casts all over the place. I don't think that
> will make things clearer or more robust. I think we either leave it as
> my first patch for now or find a more robust solution with a union or
> something.
Hm. Could we just create two separate fields? It's not real clear to
me that forcing both these usages into a generic pointer buys much.
regards, tom lane
On fre, 2012-02-24 at 11:10 -0500, Tom Lane wrote: > Peter Eisentraut <peter_e@gmx.net> writes: > > On tor, 2012-02-23 at 10:17 -0500, Tom Lane wrote: > >> void * seems entirely reasonable given the two different usages, but > >> I would be happier if the patch added explicit casts whereever FH is > >> set to or used as one of these two types. > > > That would add about 70 casts all over the place. I don't think that > > will make things clearer or more robust. I think we either leave it as > > my first patch for now or find a more robust solution with a union or > > something. > > Hm. Could we just create two separate fields? It's not real clear to > me that forcing both these usages into a generic pointer buys much. It's used in confusing ways. In pg_backup_files.c _PrintFileData(), it's a compile-time decision whether FH is a FILE or a gzFile: #ifdef HAVE_LIBZ AH->FH = gzopen(filename, "rb"); #else AH->FH = fopen(filename, PG_BINARY_R); #endif But if we changed FH to be gzFile under HAVE_LIBZ, then tons of other places will complain that use fread(), fwrite(), fileno(), etc. directly on FH. Considering the volume of who complains in one way versus the other, I think _PrintFileData() is at fault. I think the best fix would be to rearrange _PrintFileData() so that it doesn't use FH at all. Instead, we could define a separate ArchiveHandle field IF that works more like OF, and then change ahwrite() to use that.
On tor, 2012-03-01 at 19:19 +0200, Peter Eisentraut wrote: > I think the best fix would be to rearrange _PrintFileData() so that it > doesn't use FH at all. Instead, we could define a separate > ArchiveHandle field IF that works more like OF, and then change > ahwrite() to use that. Here is a patch that might fix this. I haven't been able to test this properly, so this is just from tracing the code. It looks like _PrintFileData() doesn't need to use FH at all, so it could use a local file handle variable instead. Could someone verify this please?
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On Sat, Mar 17, 2012 at 3:58 AM, Peter Eisentraut <peter_e@gmx.net> wrote: > On tor, 2012-03-01 at 19:19 +0200, Peter Eisentraut wrote: >> I think the best fix would be to rearrange _PrintFileData() so that it >> doesn't use FH at all. Instead, we could define a separate >> ArchiveHandle field IF that works more like OF, and then change >> ahwrite() to use that. > > Here is a patch that might fix this. I haven't been able to test this > properly, so this is just from tracing the code. It looks like > _PrintFileData() doesn't need to use FH at all, so it could use a local > file handle variable instead. Could someone verify this please? It looks like this code can be used via the undocumented -Ff option to pg_dump. But considering this code was added in 2000 as demonstration code and has apparently never been documented, and considering also that we now have the "directory" archive format which is presumably quite a similar idea but documented and intended for production use, maybe we should just rip out pg_backup_files/archFiles altogether. pg_dump is crufty enough without supporting undocumented and obsolete options for multiple decades. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company
Robert Haas <robertmhaas@gmail.com> writes:
> maybe we should just rip out pg_backup_files/archFiles altogether.
> pg_dump is crufty enough without supporting undocumented and obsolete
> options for multiple decades.
+1
regards, tom lane
On 03/19/2012 02:53 PM, Tom Lane wrote: > Robert Haas<robertmhaas@gmail.com> writes: >> maybe we should just rip out pg_backup_files/archFiles altogether. >> pg_dump is crufty enough without supporting undocumented and obsolete >> options for multiple decades. > +1 > > Yeah, go for it. cheers andrew