[XFree86] BadAccess errors using XShmPutImage
i'm attempting to put together a simple test that creates a window, allocates a buffer in memory and using an XImage and XShmPutImage () displays it on my screen. i have a tiny piece of code that (as far as i know) does all the right things - it creates the window but when i try to display the contents of my buffer via an XImage i get a message like this: X Error of failed request: BadAccess (attempt to access private resource denied) Major opcode of failed request: 144 (MIT-SHM) Minor opcode of failed request: 3 (X_ShmPutImage) i've seen this type of problem described in the newsgroups but there don't seem to be any answers posted. i check the return from all my previous calls and they're fine. i'm using XFree86 version 4.3.0 (27 feb 2003), X Protocol version 11, rev 0, rel 6.6 and my OS is NetBSD/i386 1.6 [elf]. can anyone shed any light on this please? thanks. cp ___ XFree86 mailing list [EMAIL PROTECTED] http://XFree86.Org/mailman/listinfo/xfree86
[XFree86] BadAccess errors using XShmPutImage
i'm attempting to put together a simple test that creates a window, allocates a buffer in memory and using an XImage and XShmPutImage () displays it on my screen. i have a tiny piece of code that (as far as i know) does all the right things - it creates the window but when i try to display the contents of my buffer via an XImage i get a message like this: X Error of failed request: BadAccess (attempt to access private resource denied) Major opcode of failed request: 144 (MIT-SHM) Minor opcode of failed request: 3 (X_ShmPutImage) i've seen this type of problem described in the newsgroups but there don't seem to be any answers posted. i check the return from all my previous calls and they're fine. i'm using XFree86 version 4.3.0 (27 feb 2003), X Protocol version 11, rev 0, rel 6.6 and my OS is NetBSD/i386 1.6 [elf]. can anyone shed any light on this please? thanks. cp ___ XFree86 mailing list [EMAIL PROTECTED] http://XFree86.Org/mailman/listinfo/xfree86
Re: [XFree86] BadAccess errors using XShmPutImage
> 1) Does your X-server have SHM support? "MIT-SHM" should show up in > the list of extensions reported by xdpyinfo. Yep - that extension is listed when i run xdpyinfo. > 2) Does your operating system have SHM support? This sort of thing > is often disabled for security reasons. i'm not sure how to test this - i'm very much a x/unix novice - but after adding printf's to another library i've been looking at (SDL), it seems that it is - SDL is certainly calling XShmPutImage () successfully. > 3) Programming errors on your part? BadAccess is generated if: Very likely. >a) the server doesn't know about the segment (you called > XShmAttach on it didn't you?). Yep - I do that. >b) The size is bad, that is, the segment is too small to > contain the source you specified (or the XImage is > improperly initialized). I suspect that it is some kind of unitialized structure problem. I chopped the return value tests and the error handler out of my code for clarity and tacked it on the end of this message - might be something obvious. Thanks. cp snip shmInfo.shmid = shmget ( IPC_PRIVATE, windowWidth * windowDepthBytes * windowHeight, IPC_CREAT | 0777 ); shmInfo.shmaddr = (char *)shmat ( shmInfo.shmid, 0, 0); shminfo.readOnly = False; XShmAttach ( display, &shmInfo ); XSync ( display, True ); shmctl ( shmInfo.shmid, IPC_RMID, NULL ); pixels = shmInfo.shmaddr; ximage = XShmCreateImage ( display, DefaultVisual ( display, screen ), windowDepth, ZPixmap, shmInfo.shmaddr, &shmInfo, windowWidth, windowHeight ); XShmPutImage ( display, window, DefaultGC ( display, screen ), ximage, 0, 0, 0, 0, windowWidth, windowHeight, False ); -- > > i'm attempting to put together a simple test that creates a window, allocates a > > buffer in > > memory and using an XImage and XShmPutImage () displays it on my screen. > > > > i have a tiny piece of code that (as far as i know) does all the right things - it > > creates > the > > window but when i try to display the contents of my buffer via an XImage i get a > > message > like > > this: > > > > X Error of failed request: BadAccess (attempt to access private resource denied) > > Major opcode of failed request: 144 (MIT-SHM) > > Minor opcode of failed request: 3 (X_ShmPutImage) > > > > i've seen this type of problem described in the newsgroups but there don't seem to > > be any > > answers posted. > > > > i check the return from all my previous calls and they're fine. > > > > i'm using XFree86 version 4.3.0 (27 feb 2003), X Protocol version 11, rev 0, rel > > 6.6 and > my OS > > is NetBSD/i386 1.6 [elf]. ___ XFree86 mailing list [EMAIL PROTECTED] http://XFree86.Org/mailman/listinfo/xfree86
Re: [XFree86] BadAccess errors using XShmPutImage
Many thanks Mark - that was exactly the problem - works perfectly now. >It's likely that you're not handling the padding correctly. > Is (ximage->bytes_per_line == windowWidth * windowDepthBytes) ? > >In general, I like to create the XImage first and then allocate > the data later. That saves you from having to do the work of > finding out what the padding is supposed to be. That is, pass > NULL for the data field in XShmCreateImage. Then shmget with > (ximage->height * ximage->bytes_per_line), then fill in > ximage->data with the value returned by shmat. Eg: > > ximage = XShmCreateImage(..., &shminfo); > shminfo.shmid = shmget (.., ximage->height * ximage->bytes_per_line, ...); > shminfo.shmaddr = ximage->data = shmat(shminfo.shmid, 0, 0); > shminfo.readOnly = False; > XShmAttach (display, &shminfo); > >So the pitch you should use is ximage->bytes_per_line. You > can get that independently by looking up pixmap formats, but it's > easier to just have XShmCreateImage fill it in for you. > > Mark. > > > > On Mon, 3 Nov 2003, Callum Prentice wrote: > > > > 1) Does your X-server have SHM support? "MIT-SHM" should show up in > > > the list of extensions reported by xdpyinfo. > > > > Yep - that extension is listed when i run xdpyinfo. > > > > > 2) Does your operating system have SHM support? This sort of thing > > > is often disabled for security reasons. > > > > i'm not sure how to test this - i'm very much a x/unix novice - but after adding > > printf's > to > > another library i've been looking at (SDL), it seems that it is - SDL is certainly > > calling > > XShmPutImage () successfully. > > > > > 3) Programming errors on your part? BadAccess is generated if: > > > > Very likely. > > > > >a) the server doesn't know about the segment (you called > > > XShmAttach on it didn't you?). > > > > Yep - I do that. > > > > >b) The size is bad, that is, the segment is too small to > > > contain the source you specified (or the XImage is > > > improperly initialized). > > > > I suspect that it is some kind of unitialized structure problem. > > > > I chopped the return value tests and the error handler out of my code for clarity > > and > tacked > > it on the end of this message - might be something obvious. > > > > Thanks. > > > > cp > > > > > > snip > > shmInfo.shmid = shmget ( IPC_PRIVATE, windowWidth * windowDepthBytes * > > windowHeight, > IPC_CREAT > > | 0777 ); > > shmInfo.shmaddr = (char *)shmat ( shmInfo.shmid, 0, 0); > > shminfo.readOnly = False; > > > > XShmAttach ( display, &shmInfo ); > > > > XSync ( display, True ); > > > > shmctl ( shmInfo.shmid, IPC_RMID, NULL ); > > > > pixels = shmInfo.shmaddr; > > > > ximage = XShmCreateImage ( display, DefaultVisual ( display, screen ), windowDepth, > ZPixmap, > > shmInfo.shmaddr, &shmInfo, windowWidth, windowHeight ); > > > > XShmPutImage ( display, window, DefaultGC ( display, screen ), ximage, 0, 0, 0, 0, > > windowWidth, windowHeight, False ); > > > > -- > > > > > > > > > > > > > > i'm attempting to put together a simple test that creates a window, allocates > > > > a buffer > in > > > > memory and using an XImage and XShmPutImage () displays it on my screen. > > > > > > > > i have a tiny piece of code that (as far as i know) does all the right things > > > > - it > creates > > > the > > > > window but when i try to display the contents of my buffer via an XImage i get > > > > a > message > > > like > > > > this: > > > > > > > > X Error of failed request: BadAccess (attempt to access private resource > > > > denied) > > > > Major opcode of failed request: 144 (MIT-SHM) > > > > Minor opcode of failed request: 3 (X_ShmPutImage) > > > > > > > > i've seen this type of problem described in the newsgroups but there don't > > > > seem to be > any > > > > answers posted. > > > > > > > > i check the return from all my previous calls and they're fine. > > > > > > > > i'm using XFree86 version 4.3.0 (27 feb 2003), X Protocol version 11, rev 0, > > > > rel 6.6 > and > > > my OS > > > > is NetBSD/i386 1.6 [elf]. > > > ___ XFree86 mailing list [EMAIL PROTECTED] http://XFree86.Org/mailman/listinfo/xfree86
[XFree86] XShmSegmentInfo issues
i have a methods in a class to create a shared memory x image - it creates and stores an xImage in the usual way: XShmSegmentInfo shminfo; ximage = XShmCreateImage(..., &shminfo); shminfo.shmid = shmget (.., ximage->height * ximage->bytes_per_line, ...); shminfo.shmaddr = ximage->data = shmat(shminfo.shmid, 0, 0); shminfo.readOnly = False; XShmAttach (display, &shminfo); i call this method in several places and only call XShmPutImage on the xImage later in my code. i get an X error: "X Error of failed request: BadValue (integer parameter out of range for operation) Major opcode of failed request: 144 (MIT-SHM) Minor opcode of failed request: 3 (X_ShmPutImage)" which appears to be because the shared segment info has changed. if i save the shminfo each time and then re-attach it to the display before i call XShmPutImage, i still get the problem. any ideas ? what is the right thing to do here. also - in the code i'm using there is a call to: shmctl ( shmInfo.shmid, IPC_RMID, NULL ); just after it's created - surely this is wrong and i shouldn't remeove the sgm segment until my program is finishing. thanks in advance as always. ___ XFree86 mailing list [EMAIL PROTECTED] http://XFree86.Org/mailman/listinfo/xfree86
Re: [XFree86] XShmSegmentInfo issues
>I think you've misinterpreted this. Aside from corruption of > the ximage data structure, the only time BadValue is returned > is if your source rectangle passed to XShmPutImage lies outside > of the XImage (or if you pass junk for the send_event). Check > your dimensions passed to XShmPutImage. that's odd then - if a rearrange my code so i call create 1 then write 1 then create 2 then write 2 it works perfectly. if i call create 1 create 2 write 1 write 2 it fails with the X error i mentioned. (where 'create' does all the shm stuff and creation of the ximage and 'write' does the 'XShmPutImage' so i don't need to save/restone any of the XShmSegmentInfo then ? >Segments don't disappear until after they are removed and the last > process attaching to them has detached. Even if you remove it, it > will not go away until after you detach. When your program quits > or crashes, it detaches automatically. However, it does not get > removed automatically, so if the app quits or crashes before removing > the segment, the segment will get leaked. That's why it's common > practice to attach and then remove a segment. thanks for that clarification - excellent. ___ XFree86 mailing list [EMAIL PROTECTED] http://XFree86.Org/mailman/listinfo/xfree86
Re: [XFree86] XShmSegmentInfo issues
that's the conclusion i came to late last night too. now, for each of my XImage helper class instances, i declare a XShmSegmentInfo* in the ctor and point it to a new'd buffer so it hangs until the class dtor gets rid of it as my app is ending. seems to work okay for now. > Looking through the code, it looks like Xlib stores a pointer > to the shminfo. I didn't realize it did that. That would imply > that each XImage needs a XShmSegmentInfo that sticks around for the > life of the XImage. > > It impresses me that it is a mistake that it did this rather > than copying the contents of the XShmSegmentInfo. I'm not sure > why it was implemented that way. I don't think we have any > XShm man pages. If we did, hopefully, they would mention something > like that. > > The error must be that the first XImage ends up with the second > XImage's data and subsequently the operation appears to be addressing > outside of the shared memory segment, so the BadValue error happens. ___ XFree86 mailing list [EMAIL PROTECTED] http://XFree86.Org/mailman/listinfo/xfree86
