What is the best way to get BSD drive names on macOS (Swift)?

Question

What's the best way I can get a list of BSD names of all USB devices (and maybe including internal Mac drives) without using a diskutil CLI wrapper?

I don't want to use any wrappers that interact with the CLI interface, as this way of interacting is quite slow and unreliable:

^{This is an example of why I'm not happy with using CLI wrappers

(Compare 'Time elapsed for DiskUtil CLI Wrapper.' and 'Time elapsed for Disk Arbitration')}

What is the best way to implement the solution for my problem?
Use the data from IOReg?
If yes, how can I get a list of BSD names of connected devices using it?

Here is an example what I want to get:

["disk0", "disk0s1", "disk0s2", "disk0s3", "disk1", "disk1s1", "disk1s2", "disk1s3", "disk1s4", "disk2", "disk2s1", "disk2s2", "disk3", "disk3s1", "disk3s1s1", "disk3s2", "disk3s3", "disk3s4", "disk3s5", "disk3s6", "disk4", "disk4s1", "disk4s2", "disk5", "disk5s1", "disk5s2", "disk6", "disk6s1", "disk6s2", "disk10", "disk10s1", "disk10s2", "disk11", "disk11s1"]

At the moment, I have the following:

static func getMountedBSDNames() -> [String] {
    guard let session = DASessionCreate(nil) else { return [] }
    guard let mountedVolumeURLs = FileManager.default.mountedVolumeURLs(includingResourceValuesForKeys: nil) else { return [] }
    
    var BSDNames: [String] = []
    
    for volumeURL in mountedVolumeURLs {
        if let disk = DADiskCreateFromVolumePath(kCFAllocatorDefault, session, volumeURL as CFURL), let BSDName = DADiskGetBSDName(disk) {
            BSDNames.append(
                String(cString: BSDName)
            )
        }
    }
    
    return BSDNames
}

But in this case, only mounted are returning.
I want there to have even those, that were ejected

ReSophie · Accepted Answer · 2022-10-22T17:09:00.033

I achieved the desired result using the IOReg lookup method:

^{Elapsed Time}

func getDriveBSDNames() -> [String] {
    var iterator: io_iterator_t = 0

    let matching: CFDictionary = IOServiceMatching(kIOServicePlane)

    // Use 'kIOMasterPortDefault' for macOS older than 12.0 Monterey
    IOServiceGetMatchingServices(kIOMainPortDefault, matching, &iterator)
    var child: io_object_t = IOIteratorNext(iterator)
    
    var BSDNames: [String] = []
    while child > 0 {
        if let BSDNameAnyObject = IORegistryEntryCreateCFProperty(child, "BSD Name" as CFString, kCFAllocatorDefault, IOOptionBits(kIORegistryIterateRecursively)) {
            
            if let BSDNameString = (BSDNameAnyObject.takeRetainedValue() as? String), BSDNameString.starts(with: "disk") {
                BSDNames.append(
                    BSDNameString
                )
            }
        }
        
        child = IOIteratorNext(iterator)
    }
    
    return BSDNames
}

In this case, it was also necessary to filter the output of the results using:
BSDNameString.starts(with: "disk")
_{(otherwise, some unnecessary devices were added, such as en0, anpi0, llw0, etc.)}

I think you might end up with serial ports, which also have BSD names, in your list of results using this method. At minimum, pass `"IOStorage"` to `IOServiceMatching()` instead of `"IOService"` (this should also improve performance). — pmdj, Oct 23 '22 at 10:30
By the way, you can wrap your this manual iteration into a sequence, which makes it quite nice: `sequence(state: iterator, next: IOIteratorNext).prefix(while: { child in child > 0 })`. You can then use a regular `for` loop over it (instead of `while`). Even better, you can replace your loop_repeated `append` calls with a call to `map` or `compactMap`. See https://gist.github.com/amomchilov/7f53d9d7f2d20ef057be4a55871dc215 — Alexander, Oct 25 '22 at 14:07

score 1 · Answer 2 · answered Oct 23 '22 at 10:51

Note that while the Disk Arbitration framework doesn't have a function for synchronously enumerating all disks, it does effectively support asynchronous enumeration by registering a callback for disk appearance. This may or may not be useful depending on your use case - when providing the user with an interactive list of devices, this is usually exactly what you want though, as you'll automatically be notified of newly added devices.

I don't do Swift, sorry, but the following C code should be easy enough to understand to come up with something similar in other languages.

#include <DiskArbitration/DiskArbitration.h>
#include <stdio.h>

static void disk_appeared(DADiskRef disk, void* context)
{
    printf("%s\n", DADiskGetBSDName(disk) ?: "(null)");
}

int main()
{
    DASessionRef session = DASessionCreate(kCFAllocatorDefault);
    DASessionSetDispatchQueue(session, dispatch_get_main_queue());
    DARegisterDiskAppearedCallback(session, NULL, disk_appeared, NULL /*context*/);
    dispatch_main();
}

Note that the callback will also be called for APFS snapshots, which don't have a BSD name, so DADiskGetBSDName returns NULL and you'll have to do a little bit of filtering.

What is the best way to get BSD drive names on macOS (Swift)?

2 Answers2