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bind() should not return -EADDRINUSE

DISCUSSION Phillip Susi 2 participants 9 messages Dec 11, 2014

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Phillip Susi

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#0 lore raw

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Attempting to establish a connection to a remote host using the same local port, but a different remote port as the previous connection ( that is still in TIME_WAIT ) results in bind() returning -EADDRINUSE.
By changing the remote port, you avoid the conflict with the other
connection that is in TIME_WAIT, but since the remote port is not known when bind() is called, it incorrectly returns -EADDRINUSE. This check should not be done in bind(), but deferred until the remote port is known in the call to connect(), or listen().

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maintainer
#1 lore raw

From: Phillip Susi <[email protected]>
Date: Thu, 11 Dec 2014 14:19:11 -0500

Quoted 8 lines

Attempting to establish a connection to a remote host using the same local port, but a different remote port as the previous connection ( that is still in TIME_WAIT ) results in bind() returning -EADDRINUSE.
By changing the remote port, you avoid the conflict with the other
connection that is in TIME_WAIT, but since the remote port is not known when bind() is called, it incorrectly returns -EADDRINUSE. This check should not be done in bind(), but deferred until the remote port is known in the call to connect(), or listen().

Bind has to allocate and hold from everyone else on the system the local port at bind() time, so we cannot defer this decision.

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#2 lore raw

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Quoted 13 lines · David Miller

From: Phillip Susi <[email protected]> Date: Thu, 11 Dec 2014 14:19:11 -0500

Quoted 9 lines

Attempting to establish a connection to a remote host using the same local port, but a different remote port as the previous connection ( that is still in TIME_WAIT ) results in bind() returning -EADDRINUSE. By changing the remote port, you avoid the conflict with the other connection that is in TIME_WAIT, but since the remote port is not known when bind() is called, it incorrectly returns -EADDRINUSE. This check should not be done in bind(), but deferred until the remote port is known in the call to connect(), or listen().

Quoted 2 lines

Bind has to allocate and hold from everyone else on the system the local port at bind() time, so we cannot defer this decision.

What on earth for? If two processes are going to connect to different remotes using the same source, that is perfectly fine. The only contention is if two processes want to listen() with the same local addr and wildcard remote.

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maintainer
#3 lore raw

From: Phillip Susi <[email protected]>
Date: Thu, 11 Dec 2014 14:50:48 -0500

Quoted 17 lines

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Quoted 13 lines · David Miller

From: Phillip Susi <[email protected]> Date: Thu, 11 Dec 2014 14:19:11 -0500

Quoted 9 lines

Attempting to establish a connection to a remote host using the same local port, but a different remote port as the previous connection ( that is still in TIME_WAIT ) results in bind() returning -EADDRINUSE. By changing the remote port, you avoid the conflict with the other connection that is in TIME_WAIT, but since the remote port is not known when bind() is called, it incorrectly returns -EADDRINUSE. This check should not be done in bind(), but deferred until the remote port is known in the call to connect(), or listen().

Quoted 7 lines
Quoted 2 lines

Bind has to allocate and hold from everyone else on the system the local port at bind() time, so we cannot defer this decision.

What on earth for? If two processes are going to connect to different remotes using the same source, that is perfectly fine. The only contention is if two processes want to listen() with the same local addr and wildcard remote.

But you don't know ahead of time what the processes are going to do, that's the problem.

You cannot leave the port available and pretend to another process that he will be able to use it.

Port allocation failures must be signalled at bind() time.

author
#4 lore raw

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Quoted 8 lines · David Miller

But you don't know ahead of time what the processes are going to do, that's the problem.

You cannot leave the port available and pretend to another process that he will be able to use it.

Port allocation failures must be signalled at bind() time.

Says who? The man pages for both listen() and connect() say they can return EADDRINUSE.

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maintainer
#5 lore raw

From: Phillip Susi <[email protected]>
Date: Thu, 11 Dec 2014 15:17:12 -0500

Quoted 1 line

Says who?

Says multiple decades of precendence.

author
#6 lore raw

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Quoted 6 lines · David Miller

From: Phillip Susi <[email protected]> Date: Thu, 11 Dec 2014 15:17:12 -0500

Quoted 1 line

Says who?

Says multiple decades of precendence.

"It has always been broken, so it should stay broken" isn't a very compelling argument.

Would it cause programs to break if they get the error at listen() time instead of bind() time ( as the man page indicates it can )? I think not.

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maintainer
#7 lore raw

From: Phillip Susi <[email protected]>
Date: Thu, 11 Dec 2014 15:23:45 -0500

Quoted 9 lines

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Quoted 5 lines · David Miller

From: Phillip Susi <[email protected]> Date: Thu, 11 Dec 2014 15:17:12 -0500

Quoted 1 line

Says who?

Quoted 8 lines
Quoted 1 line

Says multiple decades of precendence.

"It has always been broken, so it should stay broken" isn't a very compelling argument.

Would it cause programs to break if they get the error at listen() time instead of bind() time ( as the man page indicates it can )? I think not.

You will definitely break programs that look for a locally available port by iterating over bind() calls.

Sorry, this is not changing, no matter how strongly you may wish it to.

author
#8 lore raw

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Quoted 5 lines · David Miller

You will definitely break programs that look for a locally available port by iterating over bind() calls.

Sorry, this is not changing, no matter how strongly you may wish it to.

According to this very nice post, it is how BSD does it, at least when you specify SO_REUSEADDR:

http://stackoverflow.com/a/14388707/884259

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