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AGMSRAMFileSystem
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 Published by Alexander G. M. Smith
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 Date Posted:   November 2nd, 2003
 Last Updated:   April 4th, 2004
 License: LGPL
 Downloads: 1,295 total; 196 recently
 Page Views: 15,392 total
 User Rating: awaiting 10 votes Give this application a rating
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About AGMSRAMFileSystem:
AGMSRAMFileSystem is a full BeOS file system which stores files in memory for extra speed. There are also a few nifty keen experimental features you won't find in regular file systems.

AGMSRAMFileSystem stores files in RAM rather than on disk. This makes it a bit faster than a real disk, more memory efficient than a RAM disk that simulates disk sectors (like AGMSRAMDiskDevice), but also means it forgets its contents as soon as you turn off the computer or reboot. There are also a few experimental features you won't find in regular file systems. It works, even down to the complexity of live update notification and BeOS query parsing, evaluation and optimisation, but is still unfinished due to a lack of time (or money :-).

Nifty Features

* Multithreaded design. There is a multiple readers / single writer semaphore on each open file and no global semaphore. That means that multiple programs can use the whole file system, and only ever wait if they conflict with a program that's trying to write to the same file or directory. You can get deadlocks, but it has timers and retry attempts to try to get around them. So if you get an EDEADLK error code, you're really unlucky, or more likely, have found a bug.

* Has AGMS links. These are kind of like hard links mixed with MacOS aliases and a twist of lemon. An AGMS link allows you to put a file in two or more directories - so you can put a photo of your aunt's cottage in the Aunt folder and the Cottage folder. It also supports putting directories inside multiple other directories, and even properly handles the case where a directory is (via a few other parent directories) inside itself by doing a graph traversal when it needs to rename or delete directories. The extra parent directories show up as "..." for the first one, "...." for the second, and so on. If you want to make an AGMS link then use a Terminal command like "ln /boot/home/Blah/OriginalFileName LinkName" to do it (you need the -d switch to hard link directories). See the AGMSLinkExplanation.txt file or the comments at the top of the AGMSRAMFileSystem.c file for an explanation.

* Has live update notification. Like BFS, whenever you change something an update message is sent to interested applications. Unlike BFS, it sends them every second or two when a file is being written to so that you can see the file size change in Tracker. It also sends notifications for changes to the index directories, which may overload Tracker (making it miss some updates since BeOS BLoopers by default can only have a backlog of 100 update messages).

* Has BeOS queries. This means code to parse the queries into subexpressions, then more code to optimise the order of evaluation, then yet more code to test attribute changes against the queries and send live updates. The parser language has been enhanced a bit, with <> and >< operators to look for files that have or do not have an attribute. The full query language is now documented, see the comments inside AGMSRAMFileSystem.c or File System API Notes.txt.

* Has Indices visible as directories. Now you can see what the indices are doing. Look inside .Indices/name and you will see the names of all the files in the RAM disk. Each name is shown as a symbolic link to the file (Tracker gets confused when direct links are used, so until it's rewritten…). The hexadecimal number after the attribute value is there to make the names unique, in case you have several files with the same attribute value or have an empty string as the attribute value.

* Has a multiple keyword index. If your attribute is "Make Money Fast", it will add the three words separately to the index, so you can search for "Make" or "Money" or "Fast" and it will find your file.

* Doesn't have queries as directories. I wanted to add magic directories where their contents would be the files that matched a query, with live updates as it changed. The query would be stored perhaps as the directory name, or maybe as an attribute on the directory. But time ran out…

Glitches

Tracker doesn't recognise the file system so it doesn't know where to put the trash. Need to fix Tracker and the BeOS FindTrashDirectory(DiskVolume) function, which means waiting for OpenBeOS I guess.

If you make the maximum size too big, you could add enough files to use up all the memory. It uses kernel space memory, of which about 700MB are free (if your swap file is big enough or you have that much real memory). You may also run into the BeOS memory allocation bug, where allocating hundreds of megabytes (of virtual pages) takes a while and causes other programs that are trying to get memory to fail (guess their deadlock timer was too short). That could happen if you copy several hundred megabytes to the RAM disk in one operation (unlikely, Tracker and "cp" break it up into smaller operations). Most BeOS software doesn't check for memory allocation failure, this includes the application server, and the OS, so a system crash will likely happen soon after the memory is used up or the big copy operation temporarily makes memory allocation fail.

If you find any bugs in the RAM disk, please let me know, and I'll file them away for when I have time to work on it.

Installation and Uninstallation

To install it, move the ARFSv0 file to your /boot/home/config/add-ons/kernel/file_systems directory (you can drag it to the supplied symbolic link to do that). To uninstall, delete that add-on from there. The only other program you need is AGMSFileSystemPacker, you can throw away the rest of the files if you want to. You can optionally run AGMSFileSystemPacker and click the "Install MIME Types" button. Maybe also then add a sound effect to the system sound effects.

Using It and Unfinished Gaps

To create a RAM disk, use the AGMSFileSystemPacker program. Select the Create radio button and hit the "Create FS" button. If you wish, you can change the volume name and maximum size before hitting "Create FS". Create several volumes (use different names!) if you wish to.

Internally, it just uses the mount system call with extra arguments that the file system needs (which the standard mount command doesn't let you provide, even though the extra arguments are just a text string). I was thinking of writing a replacement mount command that would let you give it the extra arguments string, but time doesn't permit…

To get rid of the RAM disk volume, unmount it (right click on the disk icon or use the command line). Or reboot. Note that the desktop umount command will fail if you have system debug logging turned on because printing out the log messages slows it down and the desktop Tracker becomes impatient (use the command line unmount instead).

If you turn on the system debug console (an option in the BeOS boot menu), it will print out lots and lots of syslog debug messages, at 19200 baud. This will make it very slow. It will still work, and you can examine the log by either using the serial port or this Terminal command: tail --retry --follow=name /var/log/syslog

AGMSFileSystemPacker is unfinished. It is a combination of an archiver (like zip) and RAM disk manager. I planed to have it recreate a RAM disk from an archive (double click on a .pafs Packed Archived File System file to make the disk appear). But I didn't get that far. Instead, it can only create an empty RAM disk. It can also compress a directory tree (a file system is also a directory) into an archive file, optionally using zlib compression (same compression technique as zip). Unlike zip, there is no file size limit! See AGMSFileSystemPacker File Format.txt for a description of the file format, which is streamed plain text (thus no size limit) if you don't use compression. However, it can't fully restore an archive yet - doesn't restore links or indices (just files, directories and attributes). The unpack to RAM disk choice is ignored. Also I haven't copied the compress-a-directory-tree into the file system code, so that unmounting a RAM disk doesn't yet automatically save the contents into a .pafs file.

AGMSRAMFSMounter is a test program which compares the operation of different file systems against a test suite. If you run it from Terminal, you can save the test results. It was used for making sure that AGMSRAMFileSystem behaved the same way as BFS, or better. Pick one of the two first options to choose the file system to test, or mount your own file system at /Test. Transient messages will flash for a few seconds, final results stay on the display.

mkindex is an enhancement of the old BeOS mkindex utility. Put it in /bin if you want to replace the old one. It's mainly useful for making an index with the multiple-keywords feature. Give the "mkindex" command with no arguments if you want to see a page full of its verbose help info.

AGMSRAMFileSystem is released under the GNU Lesser General Public License. See comments in AGMSRAMFileSystem.c for details.

- Alex (Ottawa, November 2003)
Latest Version
   
Details about this version:
A few minor bug fixes:

The virtual date modified attribute is now in seconds rather than microseconds, so it matches BFS. Internally the date modified index is still in microseconds, like BFS does too (presumably that's why it has a 64 bit number for the index).

Memory allocation has been hacked to work around some BeOS kernel memory allocation bugs. So now you should be able to mount new disks (DOS file system / disk cache failure) and open terminal windows (ptty malfunctions avoided) after the file system has been running for a while. Basically, it was filling up kernel memory space with 1MB chunks (fragmenting it too), now it uses 64MB chunks and tries to leave a 58MB hole for other kernel areas to grow into.

 
Intel Version - requires R5   (868 KB) 788 downloads
 
 
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Recent Talkback comments:
  • Wish I had time to finish this... - Alexander G M Smith
  • Patch Added for Big Query Crash - Alexander G M Smith
  • Re: portable RAM devices - Alexander G M Smith

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