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Make RandomAccess.Read*|Write* methods work with non-seekable files #96711

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Make RandomAccess.Read*|Write* methods work with non-seekable files #96711

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75360d5
add tests
adamsitnik Jan 9, 2024
ddc88b6
the actual change to public API, tests are passing on Windows (no cha…
adamsitnik Jan 9, 2024
ace2855
Unix implementation
adamsitnik Jan 9, 2024
7536707
fix the tests by accounting for partial writes and reads, remove refl…
adamsitnik Jan 10, 2024
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13 changes: 13 additions & 0 deletions src/libraries/Common/src/Interop/Unix/System.Native/Interop.ReadV.cs
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Original file line number Diff line number Diff line change
@@ -0,0 +1,13 @@
// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.

using System.Runtime.InteropServices;

internal static partial class Interop
{
internal static partial class Sys
{
[LibraryImport(Libraries.SystemNative, EntryPoint = "SystemNative_ReadV", SetLastError = true)]
internal static unsafe partial long ReadV(SafeHandle fd, IOVector* vectors, int vectorCount);
}
}
13 changes: 13 additions & 0 deletions src/libraries/Common/src/Interop/Unix/System.Native/Interop.WriteV.cs
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Original file line number Diff line number Diff line change
@@ -0,0 +1,13 @@
// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.

using System.Runtime.InteropServices;

internal static partial class Interop
{
internal static partial class Sys
{
[LibraryImport(Libraries.SystemNative, EntryPoint = "SystemNative_WriteV", SetLastError = true)]
internal static unsafe partial long WriteV(SafeHandle fd, IOVector* vectors, int vectorCount);
}
}
6 changes: 6 additions & 0 deletions src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems
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Original file line number Diff line number Diff line change
Expand Up @@ -2378,6 +2378,9 @@
<Compile Include="$(CommonPath)Interop\Unix\System.Native\Interop.PRead.cs">
<Link>Common\Interop\Unix\System.Native\Interop.PRead.cs</Link>
</Compile>
<Compile Include="$(CommonPath)Interop\Unix\System.Native\Interop.ReadV.cs">
<Link>Common\Interop\Unix\System.Native\Interop.ReadV.cs</Link>
</Compile>
<Compile Include="$(CommonPath)Interop\Unix\System.Native\Interop.PReadV.cs">
<Link>Common\Interop\Unix\System.Native\Interop.PReadV.cs</Link>
</Compile>
Expand All @@ -2390,6 +2393,9 @@
<Compile Include="$(CommonPath)Interop\Unix\System.Native\Interop.Read.cs">
<Link>Common\Interop\Unix\System.Native\Interop.Read.cs</Link>
</Compile>
<Compile Include="$(CommonPath)Interop\Unix\System.Native\Interop.WriteV.cs">
<Link>Common\Interop\Unix\System.Native\Interop.WriteV.cs</Link>
</Compile>
<Compile Include="$(CommonPath)Interop\Unix\System.Native\Interop.ReadDir.cs">
<Link>Common\Interop\Unix\System.Native\Interop.ReadDir.cs</Link>
</Compile>
Expand Down
68 changes: 44 additions & 24 deletions src/libraries/System.Private.CoreLib/src/System/IO/RandomAccess.Unix.cs
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Expand Up @@ -34,18 +34,9 @@ internal static unsafe int ReadAtOffset(SafeFileHandle handle, Span<byte> buffer
{
// Try pread for seekable files.
result = Interop.Sys.PRead(handle, bufPtr, buffer.Length, fileOffset);
if (result == -1)
if (result == -1 && NeedsNonOffsetFallback(handle))
{
// We need to fallback to the non-offset version for certain file types
// e.g: character devices (such as /dev/tty), pipes, and sockets.
Interop.ErrorInfo errorInfo = Interop.Sys.GetLastErrorInfo();

if (errorInfo.Error == Interop.Error.ENXIO ||
errorInfo.Error == Interop.Error.ESPIPE)
{
handle.SupportsRandomAccess = false;
result = Interop.Sys.Read(handle, bufPtr, buffer.Length);
}
result = Interop.Sys.Read(handle, bufPtr, buffer.Length);
}
}
else
Expand Down Expand Up @@ -77,7 +68,18 @@ internal static unsafe long ReadScatterAtOffset(SafeFileHandle handle, IReadOnly

fixed (Interop.Sys.IOVector* pinnedVectors = &MemoryMarshal.GetReference(vectors))
{
result = Interop.Sys.PReadV(handle, pinnedVectors, buffers.Count, fileOffset);
if (handle.SupportsRandomAccess)
{
result = Interop.Sys.PReadV(handle, pinnedVectors, buffers.Count, fileOffset);
if (result == -1 && NeedsNonOffsetFallback(handle))
{
result = Interop.Sys.ReadV(handle, pinnedVectors, buffers.Count);
}
}
else
{
result = Interop.Sys.ReadV(handle, pinnedVectors, buffers.Count);
}
}
}
finally
Expand Down Expand Up @@ -111,18 +113,9 @@ internal static unsafe void WriteAtOffset(SafeFileHandle handle, ReadOnlySpan<by
if (handle.SupportsRandomAccess)
{
bytesWritten = Interop.Sys.PWrite(handle, bufPtr, bytesToWrite, fileOffset);
if (bytesWritten == -1)
if (bytesWritten == -1 && NeedsNonOffsetFallback(handle))
{
// We need to fallback to the non-offset version for certain file types
// e.g: character devices (such as /dev/tty), pipes, and sockets.
Interop.ErrorInfo errorInfo = Interop.Sys.GetLastErrorInfo();

if (errorInfo.Error == Interop.Error.ENXIO ||
errorInfo.Error == Interop.Error.ESPIPE)
{
handle.SupportsRandomAccess = false;
bytesWritten = Interop.Sys.Write(handle, bufPtr, bytesToWrite);
}
bytesWritten = Interop.Sys.Write(handle, bufPtr, bytesToWrite);
}
}
else
Expand Down Expand Up @@ -198,7 +191,18 @@ internal static unsafe void WriteGatherAtOffset(SafeFileHandle handle, IReadOnly
long bytesWritten;
fixed (Interop.Sys.IOVector* pinnedVectors = &MemoryMarshal.GetReference(vectors))
{
bytesWritten = Interop.Sys.PWriteV(handle, pinnedVectors, buffersCount, fileOffset);
if (handle.SupportsRandomAccess)
{
bytesWritten = Interop.Sys.PWriteV(handle, pinnedVectors, buffersCount, fileOffset);
if (bytesWritten == -1 && NeedsNonOffsetFallback(handle))
{
bytesWritten = Interop.Sys.WriteV(handle, pinnedVectors, buffersCount);
}
}
else
{
bytesWritten = Interop.Sys.WriteV(handle, pinnedVectors, buffersCount);
}
}

FileStreamHelpers.CheckFileCall(bytesWritten, handle.Path);
Expand Down Expand Up @@ -243,5 +247,21 @@ internal static ValueTask WriteAtOffsetAsync(SafeFileHandle handle, ReadOnlyMemo

private static ValueTask WriteGatherAtOffsetAsync(SafeFileHandle handle, IReadOnlyList<ReadOnlyMemory<byte>> buffers, long fileOffset, CancellationToken cancellationToken)
=> handle.GetThreadPoolValueTaskSource().QueueWriteGather(buffers, fileOffset, cancellationToken);

private static bool NeedsNonOffsetFallback(SafeFileHandle handle)
{
// We need to fallback to the non-offset version for certain file types
// e.g: character devices (such as /dev/tty), pipes, and sockets.
Interop.ErrorInfo errorInfo = Interop.Sys.GetLastErrorInfo();
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Would it be easy for a future refactor to introduce something that resets last error before this is called? Maybe last error should be passed in so it's visible.


if (errorInfo.Error == Interop.Error.ENXIO ||
errorInfo.Error == Interop.Error.ESPIPE)
{
handle.SupportsRandomAccess = false;
return true;
}

return false;
}
}
}
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