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handle ENOBUFS when writing to VM socket #370

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merged 2 commits into from
Jul 23, 2024
Merged

handle ENOBUFS when writing to VM socket #370

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7782952
handle ENOBUFS when writing to VM socket
Luap99 Jul 17, 2024
0e970bf
test: fix broken dns TXT lookup test
Luap99 Jul 23, 2024
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18 changes: 11 additions & 7 deletions pkg/tap/switch.go
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Original file line number Diff line number Diff line change
Expand Up @@ -7,6 +7,7 @@ import (
"net"
"sync"
"sync/atomic"
"syscall"

"github.com/containers/gvisor-tap-vsock/pkg/types"
"github.com/google/gopacket"
Expand Down Expand Up @@ -167,18 +168,21 @@ func (e *Switch) txBuf(id int, conn protocolConn, buf []byte) error {
if conn.protocolImpl.Stream() {
size := conn.protocolImpl.(streamProtocol).Buf()
conn.protocolImpl.(streamProtocol).Write(size, len(buf))

if _, err := conn.Write(append(size, buf...)); err != nil {
e.disconnect(id, conn)
return err
}
} else {
buf = append(size, buf...)
}
for {
if _, err := conn.Write(buf); err != nil {
if errors.Is(err, syscall.ENOBUFS) {
// socket buffer can be full keep retrying sending the same data
// again until it works or we get a different error
// https://github.com/containers/gvisor-tap-vsock/issues/367
continue
}
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Wondering if we should use conn.SetWriteDeadline when there's ENOBUFS to be sure we're not getting into an infinite loop.
But looks good to me as is, we can refine it further if there are issues.

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that is an option I guess, my basic understanding is that could only happen if the reader side (VM process) no longer reads anything from the socket but still keeps the socket open.
Sounds rather unlikely to me but yes if this turn out to cause problems we can add a deadline later

e.disconnect(id, conn)
return err
}
return nil
}
return nil
}

func (e *Switch) disconnect(id int, conn net.Conn) {
Expand Down
6 changes: 3 additions & 3 deletions test/basic_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -74,10 +74,10 @@ var _ = ginkgo.Describe("dns", func() {
gomega.Expect(err).ShouldNot(gomega.HaveOccurred())
gomega.Expect(string(out)).To(gomega.ContainSubstring(`_ldap._tcp.google.com service = 5 0 389 ldap.google.com.`))
})
ginkgo.It("should resolve TXT for wikipedia.org", func() {
out, err := sshExec("nslookup -query=txt wikipedia.org")
ginkgo.It("should resolve TXT for crc.dev", func() {
out, err := sshExec("nslookup -query=txt crc.dev")
gomega.Expect(err).ShouldNot(gomega.HaveOccurred())
gomega.Expect(string(out)).To(gomega.ContainSubstring(`"v=spf1 -all"`))
gomega.Expect(string(out)).To(gomega.ContainSubstring(`text = "v=spf1`))
})

ginkgo.It("should resolve gateway.containers.internal", func() {
Expand Down
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