Add an environement variable to control stdio mode#759
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stdio descriptors (stdin, stdout and stderr) can be operated in various modes by win32compat code. The behavior is set very early in fd_table_initialize() by setting pio->type. In PowerShell/Win32-OpenSSH#1427 it was chosen to set pio->type to NONSOCK_SYNC_FD to resolve an I/O hang problem. Unfortunately this introduce problems for other ssh usage. sshfs-wiun uses ssh and has at leas 6 open issues for the same problem introduced by this NONSOCK_SYNC_FD change: https://github.com/winfsp/sshfs-win/issues?q=is%3Aissue+cb+%3A87 The sshfs-win workaround it to use an older ssh.exe from cygwin, which is bundled with sshfs-win. This program is unable to use ssh-agent, which is quite frustrating. And if PATH is not set to use it, sshfs-win cannot work. This change introduce an OPENSSH_STDIO_MODE environment variable that can be set to the following values: unknown, sock, nonsock, nonsock_sync. It cause pio->type to be set to UNKNOWN_FD, SOCK_FD, NONSOCK_FD, and NONSOCK_SYNC_FD respecitively. The default behavior when the variable is not set is unchanged (which means NONSOCK_SYNC_FD). Setting OPENSSH_STDIO_MODE="nonsock" lets sshfs-win work again with openssh-portable ssh.exe. ssh-agent can be used, and this is good.
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tgauth
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Nov 11, 2024
An assert(pio->type != UNKNOWN_FD) in fd_table_set() causes that case to fail early anyway.
tgauth
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Nov 14, 2024
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The change is approved, thank you, but what is now preventing it from being merged? |
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I am facing issues with ssh reliability even having tweaked the client and server keepalive options. As a workaround, I want to read a remote process ID before subsequent lines of output but I am facing buffering until the remote process has exited. I have a feeling this is a common requirement among devs who want POSIX pty-like line-buffering but get standard libc buffering when the output is a pipe. Will this functionality allow me to essentially setvbuf to unbuffer the ssh output I am receiving with C# Process API? |
manu0401
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Nov 20, 2024
Windows native OpenSSH has alternative behavior for standard I/O descriptors, which can be selected through the OPENSSH_STDIO_MODE environement variable. Setting it to "nonsock" is required for sshfs compatibility. See PowerShell/openssh-portable#759 for details.
manu0401
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Nov 20, 2024
Windows native OpenSSH has alternative behavior for standard I/O descriptors, which can be selected through the OPENSSH_STDIO_MODE environement variable. Setting it to "nonsock" is required for sshfs compatibility. See PowerShell/openssh-portable#759 for details. Subitted upstream here libfuse/sshfs#314
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hazelduvall
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May 6, 2026
* Add an environement variable to control stdio mode stdio descriptors (stdin, stdout and stderr) can be operated in various modes by win32compat code. The behavior is set very early in fd_table_initialize() by setting pio->type. In PowerShell/Win32-OpenSSH#1427 it was chosen to set pio->type to NONSOCK_SYNC_FD to resolve an I/O hang problem. Unfortunately this introduce problems for other ssh usage. sshfs-wiun uses ssh and has at leas 6 open issues for the same problem introduced by this NONSOCK_SYNC_FD change: https://github.com/winfsp/sshfs-win/issues?q=is%3Aissue+cb+%3A87 The sshfs-win workaround it to use an older ssh.exe from cygwin, which is bundled with sshfs-win. This program is unable to use ssh-agent, which is quite frustrating. And if PATH is not set to use it, sshfs-win cannot work. This change introduce an OPENSSH_STDIO_MODE environment variable that can be set to the following values: unknown, sock, nonsock, nonsock_sync. It cause pio->type to be set to UNKNOWN_FD, SOCK_FD, NONSOCK_FD, and NONSOCK_SYNC_FD respecitively. The default behavior when the variable is not set is unchanged (which means NONSOCK_SYNC_FD). Setting OPENSSH_STDIO_MODE="nonsock" lets sshfs-win work again with openssh-portable ssh.exe. ssh-agent can be used, and this is good. * Leave out UNKNOWN_FD as the possible rtpes for stdio descriptors An assert(pio->type != UNKNOWN_FD) in fd_table_set() causes that case to fail early anyway.
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stdio descriptors (stdin, stdout and stderr) can be operated in various modes by win32compat code. The behavior is set very early in fd_table_initialize() by setting pio->type.
In PowerShell/Win32-OpenSSH#1427 it was chosen to set pio->type to NONSOCK_SYNC_FD to resolve an I/O hang problem. Unfortunately this introduce problems for other ssh usage.
sshfs-wiun uses ssh and has at leas 6 open issues for the same problem introduced by this NONSOCK_SYNC_FD change: https://github.com/winfsp/sshfs-win/issues?q=is%3Aissue+cb+%3A87
The sshfs-win workaround it to use an older ssh.exe from cygwin, which is bundled with sshfs-win. This program is unable to use ssh-agent, which is quite frustrating. And if PATH is not set to use it, sshfs-win cannot work.
This change introduce an OPENSSH_STDIO_MODE environment variable that can be set to the following values: unknown, sock, nonsock, nonsock_sync. It cause pio->type to be set to UNKNOWN_FD, SOCK_FD, NONSOCK_FD, and NONSOCK_SYNC_FD respecitively. The default behavior when the variable is not set is unchanged (which means NONSOCK_SYNC_FD).
Setting OPENSSH_STDIO_MODE="nonsock" lets sshfs-win work again with openssh-portable ssh.exe. ssh-agent can be used, and this is good.
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