From: Max Reitz <mreitz@redhat.com>
To: qemu-devel@nongnu.org, virtio-fs@redhat.com
Cc: "Dr . David Alan Gilbert" <dgilbert@redhat.com>,
Stefan Hajnoczi <stefanha@redhat.com>,
Max Reitz <mreitz@redhat.com>
Subject: [PATCH 1/9] virtiofsd: Add TempFd structure
Date: Fri, 4 Jun 2021 18:13:29 +0200 [thread overview]
Message-ID: <20210604161337.16048-2-mreitz@redhat.com> (raw)
In-Reply-To: <20210604161337.16048-1-mreitz@redhat.com>
We are planning to add file handles to lo_inode objects as an
alternative to lo_inode.fd. That means that everywhere where we
currently reference lo_inode.fd, we will have to open a temporary file
descriptor that needs to be closed after use.
So instead of directly accessing lo_inode.fd, there will be a helper
function (lo_inode_fd()) that either returns lo_inode.fd, or opens a new
file descriptor with open_by_handle_at(). It encapsulates this result
in a TempFd structure to let the caller know whether the FD needs to be
closed after use (opened from the handle) or not (copied from
lo_inode.fd).
By using g_auto(TempFd) to store this result, callers will not even have
to care about closing a temporary FD after use. It will be done
automatically once the object goes out of scope.
Signed-off-by: Max Reitz <mreitz@redhat.com>
---
tools/virtiofsd/passthrough_ll.c | 49 ++++++++++++++++++++++++++++++++
1 file changed, 49 insertions(+)
diff --git a/tools/virtiofsd/passthrough_ll.c b/tools/virtiofsd/passthrough_ll.c
index 49c21fd855..a4674aba80 100644
--- a/tools/virtiofsd/passthrough_ll.c
+++ b/tools/virtiofsd/passthrough_ll.c
@@ -174,6 +174,28 @@ struct lo_data {
int user_killpriv_v2, killpriv_v2;
};
+/**
+ * Represents a file descriptor that may either be owned by this
+ * TempFd, or only referenced (i.e. the ownership belongs to some
+ * other object, and the value has just been copied into this TempFd).
+ *
+ * The purpose of this encapsulation is to be used as g_auto(TempFd)
+ * to automatically clean up owned file descriptors when this object
+ * goes out of scope.
+ *
+ * Use temp_fd_steal() to get an owned file descriptor that will not
+ * be closed when the TempFd goes out of scope.
+ */
+typedef struct {
+ int fd;
+ bool owned; /* fd owned by this object? */
+} TempFd;
+
+#define TEMP_FD_INIT ((TempFd) { .fd = -1, .owned = false })
+
+static void temp_fd_clear(TempFd *temp_fd);
+G_DEFINE_AUTO_CLEANUP_CLEAR_FUNC(TempFd, temp_fd_clear);
+
static const struct fuse_opt lo_opts[] = {
{ "sandbox=namespace",
offsetof(struct lo_data, sandbox),
@@ -249,6 +271,33 @@ static struct lo_data *lo_data(fuse_req_t req)
return (struct lo_data *)fuse_req_userdata(req);
}
+/**
+ * Clean-up function for TempFds
+ */
+static void temp_fd_clear(TempFd *temp_fd)
+{
+ if (temp_fd->owned) {
+ close(temp_fd->fd);
+ *temp_fd = TEMP_FD_INIT;
+ }
+}
+
+/**
+ * Return an owned fd from *temp_fd that will not be closed when
+ * *temp_fd goes out of scope.
+ *
+ * (TODO: Remove __attribute__ once this is used.)
+ */
+static __attribute__((unused)) int temp_fd_steal(TempFd *temp_fd)
+{
+ if (temp_fd->owned) {
+ temp_fd->owned = false;
+ return temp_fd->fd;
+ } else {
+ return dup(temp_fd->fd);
+ }
+}
+
/*
* Load capng's state from our saved state if the current thread
* hadn't previously been loaded.
--
2.31.1
next prev parent reply other threads:[~2021-06-04 17:13 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-04 16:13 [PATCH 0/9] virtiofsd: Allow using file handles instead of O_PATH FDs Max Reitz
2021-06-04 16:13 ` Max Reitz [this message]
2021-06-04 16:13 ` [PATCH 2/9] virtiofsd: Use lo_inode_open() instead of openat() Max Reitz
2021-06-04 16:13 ` [PATCH 3/9] virtiofsd: Add lo_inode_fd() helper Max Reitz
2021-06-04 16:13 ` [PATCH 4/9] virtiofsd: Let lo_fd() return a TempFd Max Reitz
2021-06-04 16:13 ` [PATCH 5/9] virtiofsd: Let lo_inode_open() " Max Reitz
2021-06-04 16:13 ` [PATCH 6/9] virtiofsd: Add lo_inode.fhandle Max Reitz
2021-06-04 16:13 ` [PATCH 7/9] virtiofsd: Add inodes_by_handle hash table Max Reitz
2021-06-04 16:13 ` [PATCH 8/9] virtiofsd: Optionally fill lo_inode.fhandle Max Reitz
2021-06-08 10:43 ` Dr. David Alan Gilbert
2021-06-08 11:05 ` Max Reitz
2021-06-04 16:13 ` [PATCH 9/9] virtiofsd: Add lazy lo_do_find() Max Reitz
2021-06-04 21:17 ` [Virtio-fs] [PATCH 0/9] virtiofsd: Allow using file handles instead of O_PATH FDs Connor Kuehl
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