On 26 Oct 2008, at 16:37, Gregory Weston wrote:

Amusingly, when you register an unmount or eject approval function with DiskArbitration, that function gets invoked *after* NSWorkspace sends its didUnmount notification. How's that for a lead-in anecdote?

So anyway, I'm looking to react to the imminent or even potential departure of a volume. Some way I can know that a volume will (or probably will) be taken away from me in the near future but with enough lead time that I can reliably make one or two quick function calls against it. Any thoughts? I'm not worried about abrupt disconnects like the user yanking the cable on an external drive. Just looking for the tiniest smidgen of warning for orderly unmounts.

Specifically, I'm looking for the opportunity to call FSGetCatalogInfo on the mount point and then FSGetVolumeInfo on the volume reference number I got back from the first call.

Have you actually tried using DiskArbitration unmount approval callbacks? I decided to give it a go and was able to successfully call FSGetVolumeInfo in the callback. Tested with OS X 10.5.5 and Xcode 3.1.1. The full project is at http://www.devrx.org/software/osx/DiskArbitrationTest.zip , here's the important bits:

@implementation FDDAController

static DADissenterRef DiskUnmountApprovalCallback(DADiskRef disk, void *context)
{
    //FDDAController *self = (FDDAController *)context;

    OSStatus status;
    OSErr err;

    CFDictionaryRef diskDescription = DADiskCopyDescription(disk);
NSLog(@"DiskUnmountApprovalCallback diskDescription = %@", diskDescription);

    NSDictionary *nsDiskDescription = (NSDictionary *)diskDescription;
    NSURL *volumeURL = [nsDiskDescription valueForKey:@"DAVolumePath"];
    if (![volumeURL isFileURL])
    {
        NSLog(@"Error: volume URL %@ is not a file URL!", volumeURL);
        goto EXIT1;
    }

    NSString *volumePath = [volumeURL path];
    const char *utf8VolumePath = [volumePath UTF8String];
    FSRef volumeFSRef;
if ((status = FSPathMakeRef((UInt8 *)utf8VolumePath, &volumeFSRef, (Boolean *)NULL)) != noErr)
    {
        NSLog(@"FDPathMakeRef error: %d", status);
        goto EXIT1;
    }

    FSCatalogInfo catalogInfo;
if ((err = FSGetCatalogInfo(&volumeFSRef, kFSCatInfoVolume, &catalogInfo, NULL, NULL, NULL)) != noErr)
    {
        NSLog(@"FSGetCatalogInfo error: %d", err);
        goto EXIT1;
    }

    FSVolumeInfo volumeInfo;
    if ((err = FSGetVolumeInfo(catalogInfo.volume,
                               0, NULL,
                               kFSVolInfoGettableInfo, &volumeInfo,
                               NULL,
                               NULL)) != noErr)
    {
        NSLog(@"FSGetVolumeInfo error: %d", err);
        goto EXIT1;
    }

NSLog(@"totalBytes = %llu, freeBytes = %llu, blockSize = %u", volumeInfo.totalBytes, volumeInfo.freeBytes, volumeInfo.blockSize);

EXIT1:
    CFRelease(diskDescription);

    return NULL;
}

- (void)awakeFromNib
{
    NSLog(@"FDDAController awakeFromNib");

    daApprovalSession = DAApprovalSessionCreate(kCFAllocatorDefault);
    DAApprovalSessionScheduleWithRunLoop(daApprovalSession,
[[NSRunLoop mainRunLoop] getCFRunLoop],
                                         kCFRunLoopCommonModes);
    DARegisterDiskUnmountApprovalCallback(daApprovalSession,
                                          NULL,
                                          &DiskUnmountApprovalCallback,
                                          (void *)self);
    NSLog(@"finished registering callbacks");
}

- (void)dealloc
{
DAUnregisterApprovalCallback(daApprovalSession, DiskUnmountApprovalCallback, self);

    DAApprovalSessionUnscheduleFromRunLoop(daApprovalSession,
[[NSRunLoop mainRunLoop] getCFRunLoop],
                                           kCFRunLoopCommonModes);

    CFRelease(daApprovalSession);
    [super dealloc];
}

Francis

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