April 2008 - Darwin-dev - lists.apple.com

Re: Seek to end?
by Nathaniel Gray 06 Apr '08

06 Apr '08

site_archiver(a)lists.apple.com Delivered-To: darwin-dev(a)lists.apple.com Cheers, -n8 -- >>>-- Nathaniel Gray -- Caltech Computer Science ------> >>>-- Mojave Project -- http://mojave.cs.caltech.edu --> _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-dev mailing list (Darwin-dev(a)lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/darwin-dev/site_archiver%40lists.app… Peter Seebach writes: Prototypes. Compile with warnings on; you'd have gotten the answer from the compiler. Ah, thanks! No cookie for the genius who decided that "Treat Missing Function Prototypes as Errors" should be *disabled* in Xcode by default... This email sent to site_archiver(a)lists.apple.com

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Re: lseek to end?
by seebs＠seebs.net 06 Apr '08

06 Apr '08

site_archiver(a)lists.apple.com Delivered-To: darwin-dev(a)lists.apple.com In message <053B7261-343F-4F22-8A26-85D84A6DE763(a)caltech.edu>, Nathaniel Gray w rites: >Can anybody help me understand why this fails every time with EINVAL >on Leopard x86? Prototypes. Compile with warnings on; you'd have gotten the answer from the compiler. >#include <stdio.h> >#include <fcntl.h> >#include <assert.h> You don't have unistd.h. > off_t s = lseek(fd, 0, SEEK_END); Since you didn't declare it, lseek is declared implicit int, and 0 is not promoted to 64 bits. The rest follows. -s _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-dev mailing list (Darwin-dev(a)lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/darwin-dev/site_archiver%40lists.app… This email sent to site_archiver(a)lists.apple.com

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lseek to end?
by Nathaniel Gray 06 Apr '08

06 Apr '08

site_archiver(a)lists.apple.com Delivered-To: darwin-dev(a)lists.apple.com #include <stdio.h> #include <fcntl.h> #include <assert.h> int main(int argc, char *argv[]) { int fd = open(argv[0], O_RDWR); assert(fd != -1); off_t s = lseek(fd, 0, SEEK_END); if (s == -1) { perror("Couldn't seek to end"); return 1; } printf("File is %d bytes\n", s); return 0; } Thanks, -n8 PS: Please CC me with replies. -- >>>-- Nathaniel Gray -- Caltech Computer Science ------> >>>-- Mojave Project -- http://mojave.cs.caltech.edu --> _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-dev mailing list (Darwin-dev(a)lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/darwin-dev/site_archiver%40lists.app… Can anybody help me understand why this fails every time with EINVAL on Leopard x86? This email sent to site_archiver(a)lists.apple.com

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Re: SHM_INFO and SHM_STAT
by Terry Lambert 02 Apr '08

02 Apr '08

site_archiver(a)lists.apple.com Delivered-To: darwin-dev(a)lists.apple.com Use standard APIs instead: ? Hope this was the information you needed. -- Terry _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-dev mailing list (Darwin-dev(a)lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/darwin-dev/site_archiver%40lists.app… On Apr 2, 2008, at 3:33 AM, Christof Rath <c.rath(a)student.tugraz.at> wrote: Hello Terry (and the rest of you), I sent your notes to the lead programmer of the framework I try to compile and got a reply that I would love to forward to you: <http://www.opengroup.org/onlinepubs/009695399/functions/shmctl.html > SHM_INFO you can emulate by writing code to popen the "ipcs" command. You are better off using ftok(0 to identify a shared memory segment key specifically, rather than trying to figure out the next available one. It's pretty bad that the ipcs code is not available to use the API that this program uses directly. What we are trying to do is enumerate all existing shared memory segment for peeking into them to see if we find our own shared memory segments. I suspected as much, which is why I suggested that ftok(), which is the industry best common practice for establishing a rendezvous for System V shared memory segments, be used instead. Other methods are to mmap() a well known file, use shm_open() on a well known (to your program) name, pass around a handle to a shared vm region using Mach APIs, etc.. The method we use to iterate shared memory segments for ipcs is sysctl using a structure containing a cursor field. It's possible to use this directly, but since the cursor is in a data structure that has to be modified by user space on the way in, the approach is limited to the root user, due to the nature of sysctl. This SPI has changed twice so far, and will likely change again for architecture support reasons. Because of this, the SPI contract is between the kernel and the ipcs program in user space, and not with user applications. To obtain the structure involved, you will need to obtain xnu sources. Additionally, access to shared memory segments is restricted by an ipc_perm structure, per the UNIX standard. Clearly, if you were running as root, you could ignore this and nose around in all the segments trying to find yours - but would you trust someone else to so the same with your segments, containing potentially sensitive data, and knowing they might make a mistake? SHM_STAT does not appear to be a useful API, since it only returns an array index, and that array index could in no way be useful to you directly, since you can't access the array which is being indexed by the number which would be returned. Wrong. It is helpful for the mentioned enumeration. For IPC_STAT you need a shmem ID, for SHM_STAT you can use the kernel-internal array index and you can get the length of the array with SHM_INFO and thus you can iterate really smoothly over all existing shared memory segments. This code works on FreeBSD as well which makes it especially cumbersome that Apple left this part of useful code out. The SHM_STAT exposes internal kernel structures which can and do change on software updates. It is a design error to expose such structures for use in third party program, even for Linux or FreeBSD. Doing so damages either (a) the ability to maintain binary compatibility with third party software or (b) the lattitude of the OS vendor to transparently fix bugs. SHM_LOCK/SHM_UNLOCK are really dangerous, since you are asking that the memory region be wired down. You can ask for this via the standard interfaces mlock() and munlock(). Typically, this is a bad idea. Wiring down physical memory is constrained by administrative limits which can not be bypassed, so if you ask for too much, you will get none. These interfaces work equally well in Linux, and are more portable. True, but there are situation when you need it in a real-time robotics domain were you cannot afford if your critical data section has been swapped away... There are so many scheduler, ACPI, SMI, power and thermal management, and other assumptions in this statement, I have no idea how to go about addressing them... All I need is the ipcs source or a note on how this program enumerates all existing shared memory segments. See above for both this information, and why it undesirable for you to use it from a code portability perspective, as well as industry best common practice, which would allow you to avoid the need. This email sent to site_archiver(a)lists.apple.com

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Re: SHM_INFO and SHM_STAT
by Christof Rath 02 Apr '08

02 Apr '08

site_archiver(a)lists.apple.com Delivered-To: darwin-dev(a)lists.apple.com Dkim-signature: v=1; a=rsa-sha256; c=relaxed/simple; d=tugraz.at; s=mailrelay; t=1207132397; bh=bIYQLqU9ddMrLmoYF8T1gxg+m6LUETQB19R/p 5S10hA=; h=Cc:Message-Id:From:To:In-Reply-To:Content-Type: Content-Transfer-Encoding:Mime-Version:Subject:Date:References: X-Mailer; b=dvsbZxXK5eFBaq0heQZ76Ihlpue7PCXSk7Dl23tm+1RURtlpRgLUHh aaYaI8EuEfhkv6DnU2y2ZhujMxAAaH7XQtSuimWFkqYhY6mAm5jLs27d5MIxZlGcoy4 Jk2fsQriJqpGTHWSG3AgIMZMU/Y3U5KG8j//mcYgV3aKarZDbU= Hello Terry (and the rest of you), Use standard APIs instead: <http://www.opengroup.org/onlinepubs/009695399/functions/shmctl.html> ? Tim and Christof _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-dev mailing list (Darwin-dev(a)lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/darwin-dev/site_archiver%40lists.app… I sent your notes to the lead programmer of the framework I try to compile and got a reply that I would love to forward to you: SHM_INFO you can emulate by writing code to popen the "ipcs" command. You are better off using ftok(0 to identify a shared memory segment key specifically, rather than trying to figure out the next available one. It's pretty bad that the ipcs code is not available to use the API that this program uses directly. What we are trying to do is enumerate all existing shared memory segment for peeking into them to see if we find our own shared memory segments. SHM_STAT does not appear to be a useful API, since it only returns an array index, and that array index could in no way be useful to you directly, since you can't access the array which is being indexed by the number which would be returned. Wrong. It is helpful for the mentioned enumeration. For IPC_STAT you need a shmem ID, for SHM_STAT you can use the kernel-internal array index and you can get the length of the array with SHM_INFO and thus you can iterate really smoothly over all existing shared memory segments. This code works on FreeBSD as well which makes it especially cumbersome that Apple left this part of useful code out. SHM_LOCK/SHM_UNLOCK are really dangerous, since you are asking that the memory region be wired down. You can ask for this via the standard interfaces mlock() and munlock(). Typically, this is a bad idea. Wiring down physical memory is constrained by administrative limits which can not be bypassed, so if you ask for too much, you will get none. These interfaces work equally well in Linux, and are more portable. True, but there are situation when you need it in a real-time robotics domain were you cannot afford if your critical data section has been swapped away... All I need is the ipcs source or a note on how this program enumerates all existing shared memory segments. This email sent to site_archiver(a)lists.apple.com

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Re: SHM_INFO and SHM_STAT
by Terry Lambert 02 Apr '08

02 Apr '08

site_archiver(a)lists.apple.com Delivered-To: darwin-dev(a)lists.apple.com The four commands in use: SHM_INFO, SHM_STAT, SHM_LOCK and SHM_UNLOCK a code fragment: [...] struct shmid_ds shm_info; max_id = shmctl( 0, SHM_INFO, &shm_info ); if (max_id >= 0) { for ( int i = 0; (_memptr == NULL) && (i <= max_id); ++i ) { shm_id = shmctl( i, SHM_STAT, &shm_segment ); if ( shm_id < 0 ) continue; [...] or: [...] if (swapable) { shmctl(__shared_mem_id, SHM_UNLOCK, NULL); } else { shmctl(__shared_mem_id, SHM_LOCK, NULL); } [...] Use standard APIs instead: <http://www.opengroup.org/onlinepubs/009695399/functions/shmctl.html> ? -- Terry _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-dev mailing list (Darwin-dev(a)lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/darwin-dev/site_archiver%40lists.app… On Mar 31, 2008, at 11:23 AM, Christof Rath wrote: Hey there, I try to compile a robot framework that is written for Linux. My problem is, that it uses shmctl() commands that aren't defined in shm.h (like on linux systems). is there a workaround? Can anybody tell me how to access this information? SHM_INFO you can emulate by writing code to popen the "ipcs" command. You are better off using ftok(0 to identify a shared memory segment key specifically, rather than trying to figure out the next available one. SHM_STAT does not appear to be a useful API, since it only returns an array index, and that array index could in no way be useful to you directly, since you can't access the array which is being indexed by the number which would be returned. SHM_LOCK/SHM_UNLOCK are really dangerous, since you are asking that the memory region be wired down. You can ask for this via the standard interfaces mlock() and munlock(). Typically, this is a bad idea. Wiring down physical memory is constrained by administrative limits which can not be bypassed, so if you ask for too much, you will get none. These interfaces work equally well in Linux, and are more portable. This email sent to site_archiver(a)lists.apple.com

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