How to get file information using Mono on Linux

Question

Using Mono, I want to get various bits of information about files on Linux systems.

In particular, I want to get file attributes, file permissions, owner and whether the file is an actual file or a link of some type.

In Windows I would use FileInfo.Attributes to get file attributes - but this just returns FileAttributes.Normal on Linux, even though the lsattr command reports ----ia-------e-- (for example).

In Windows I would use FileSecurity to get the owner and file permissions - but this throws with PlatformNotSupportedException on Linux.

Answer 1

You might want to conditionally use classes from Mono.Unix, in particular UnixFileInfo, depending on Environment.OSVersion.Platform.

Answer 2

I had the same request, and had to hack a solution by myself, hope you'll like it :)

using System;
using System.Runtime.InteropServices;

partial class FileProvider
{
    private const uint IOCPARM_MASK = 0x7f; /* parameters must be < 128 bytes */
    private const uint IOC_VOID = 0x20000000; /* no parameters */
    private const uint IOC_IN = 0x40000000; /* copy out parameters */
    private const uint IOC_OUT = 0x80000000; /* copy in parameters */
    private const uint IOC_INOUT = (IOC_IN | IOC_OUT);
    /* the 0x20000000 is so we can distinguish new ioctl's from old */

    private static uint _IOXXX(uint ioc, int x, int y, int l)
    {
        return ioc | (((uint)l & IOCPARM_MASK) << 16) | ((uint)x << 8) | (uint)y;
    }

    private static uint _IO(int x, int y)
    {
        return _IOXXX(IOC_VOID, x, y, 0);
    }

    private static int SizeOf<T>()
    {
        var type = typeof (T);
        if (type.IsEnum)
            return Marshal.SizeOf(type.GetEnumUnderlyingType());
        return Marshal.SizeOf(type);
    }

    private static uint _IOR<T>(int x, int y)
    {
        return _IOXXX(IOC_OUT, x, y, SizeOf<T>());
    }

    private static uint _IOW<T>(int x, int y)
    {
        return _IOXXX(IOC_IN, x, y, SizeOf<T>());
    }

    private static uint _IORW<T>(int x, int y)
    {
        return _IOXXX(IOC_INOUT, x, y, SizeOf<T>());
    }

    public static uint EXT2_IOC_GETFLAGS
    {
        get { return _IOR<IOC_FLAGS>('f', 1); }
    }

    public static uint EXT2_IOC_SETFLAGS
    {
        get { return _IOW<IOC_FLAGS>('f', 2); }
    }

    [Flags]
    private enum IOC_FLAGS : long
    {
        EXT2_SECRM_FL = 0x00000001, /* Secure deletion */
        EXT2_UNRM_FL = 0x00000002, /* Undelete */
        EXT2_COMPR_FL = 0x00000004, /* Compress file */
        EXT2_SYNC_FL = 0x00000008, /* Synchronous updates */
        EXT2_IMMUTABLE_FL = 0x00000010, /* Immutable file */
        EXT2_APPEND_FL = 0x00000020, /* writes to file may only append */
        EXT2_NODUMP_FL = 0x00000040, /* do not dump file */
        EXT2_NOATIME_FL = 0x00000080, /* do not update atime */
        /* Reserved for compression usage... */
        EXT2_DIRTY_FL = 0x00000100,
        EXT2_COMPRBLK_FL = 0x00000200, /* One or more compressed clusters */
        EXT2_NOCOMPR_FL = 0x00000400, /* Access raw compressed data */
        EXT2_ECOMPR_FL = 0x00000800, /* Compression error */
        /* End compression flags --- maybe not all used */
        EXT2_BTREE_FL = 0x00001000, /* btree format dir */
        EXT2_INDEX_FL = 0x00001000, /* hash-indexed directory */
        EXT2_IMAGIC_FL = 0x00002000,
        EXT3_JOURNAL_DATA_FL = 0x00004000, /* file data should be journaled */
        EXT2_NOTAIL_FL = 0x00008000, /* file tail should not be merged */
        EXT2_DIRSYNC_FL = 0x00010000, /* Synchronous directory modifications */
        EXT2_TOPDIR_FL = 0x00020000, /* Top of directory hierarchies*/
        EXT4_HUGE_FILE_FL = 0x00040000, /* Set to each huge file */
        EXT4_EXTENTS_FL = 0x00080000, /* Inode uses extents */
        EXT4_EA_INODE_FL = 0x00200000, /* Inode used for large EA */
        /* EXT4_EOFBLOCKS_FL 0x00400000 was here */
        FS_NOCOW_FL = 0x00800000, /* Do not cow file */
        EXT4_SNAPFILE_FL = 0x01000000, /* Inode is a snapshot */
        EXT4_SNAPFILE_DELETED_FL = 0x04000000, /* Snapshot is being deleted */
        EXT4_SNAPFILE_SHRUNK_FL = 0x08000000, /* Snapshot shrink has completed */
        EXT2_RESERVED_FL = 0x80000000, /* reserved for ext2 lib */
    }

    [DllImport("libc", EntryPoint = "ioctl", SetLastError = true)]
    private extern static int ioctl(int fd, uint request, ref IOC_FLAGS data);

Then you just need to open the file using Syscall.open, use FileProvider.ioctl with the given file descriptor and either EXT2_IOC_GETFLAGS or EXT2_IOC_SETFLAGS (you'll probably need to change some permissions too, this is a raw copy/paste) the way you want and then use Syscall.close