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Merge pull request #12687 from Mic92/handle-eagain

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libutil/file-descriptor: handle EAGAIN in read/write operations
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Jörg Thalheim 2025-03-19 22:46:05 +01:00 • committed by GitHub
commit 12ad06c104
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1 changed files with 40 additions and 4 deletions
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44
src/libutil/unix/file-descriptor.cc
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@ -5,9 +5,27 @@
#include <fcntl.h> #include <fcntl.h>
#include <unistd.h> #include <unistd.h>
#include <poll.h>
namespace nix { namespace nix {
namespace {
// This function is needed to handle non-blocking reads/writes. This is needed in the buildhook, because
// somehow the json logger file descriptor ends up beeing non-blocking and breaks remote-building.
// TODO: get rid of buildhook and remove this function again (https://github.com/NixOS/nix/issues/12688)
void pollFD(int fd, int events)
{
struct pollfd pfd;
pfd.fd = fd;
pfd.events = events;
int ret = poll(&pfd, 1, -1);
if (ret == -1) {
throw SysError("poll on file descriptor failed");
}
}
}
std::string readFile(int fd) std::string readFile(int fd)
{ {
struct stat st; struct stat st;
@ -17,14 +35,18 @@ std::string readFile(int fd)
return drainFD(fd, true, st.st_size); return drainFD(fd, true, st.st_size);
} }
void readFull(int fd, char * buf, size_t count) void readFull(int fd, char * buf, size_t count)
{ {
while (count) { while (count) {
checkInterrupt(); checkInterrupt();
ssize_t res = read(fd, buf, count); ssize_t res = read(fd, buf, count);
if (res == -1) { if (res == -1) {
if (errno == EINTR) continue; switch (errno) {
case EINTR: continue;
case EAGAIN:
pollFD(fd, POLLIN);
continue;
}
throw SysError("reading from file"); throw SysError("reading from file");
} }
if (res == 0) throw EndOfFile("unexpected end-of-file"); if (res == 0) throw EndOfFile("unexpected end-of-file");
@ -39,8 +61,15 @@ void writeFull(int fd, std::string_view s, bool allowInterrupts)
while (!s.empty()) { while (!s.empty()) {
if (allowInterrupts) checkInterrupt(); if (allowInterrupts) checkInterrupt();
ssize_t res = write(fd, s.data(), s.size()); ssize_t res = write(fd, s.data(), s.size());
if (res == -1 && errno != EINTR) if (res == -1) {
switch (errno) {
case EINTR: continue;
case EAGAIN:
pollFD(fd, POLLOUT);
continue;
}
throw SysError("writing to file"); throw SysError("writing to file");
}
if (res > 0) if (res > 0)
s.remove_prefix(res); s.remove_prefix(res);
} }
@ -56,8 +85,15 @@ std::string readLine(int fd, bool eofOk)
// FIXME: inefficient // FIXME: inefficient
ssize_t rd = read(fd, &ch, 1); ssize_t rd = read(fd, &ch, 1);
if (rd == -1) { if (rd == -1) {
if (errno != EINTR) switch (errno) {
case EINTR: continue;
case EAGAIN: {
pollFD(fd, POLLIN);
continue;
}
default:
throw SysError("reading a line"); throw SysError("reading a line");
}
} else if (rd == 0) { } else if (rd == 0) {
if (eofOk) if (eofOk)
return s; return s;