Re: [libvirt] [PATCH v8 2/7] qapi: Introduce add-fd, remove-fd, query-fdsets

This patch adds support that enables passing of file descriptors to the QEMU monitor where they will be stored in specified file descriptor sets. A file descriptor set can be used by a client like libvirt to store file descriptors for the same file. This allows the client to open a file with different access modes (O_RDWR, O_WRONLY, O_RDONLY) and add/remove the passed fds to/from an fd set as needed. This will allow QEMU to (in a later patch in this series) "open" and "reopen" the same file by dup()ing the fd in the fd set that corresponds to the file, where the fd has the matching access mode flag that QEMU requests. The new QMP commands are: add-fd: Add a file descriptor to an fd set remove-fd: Remove a file descriptor from an fd set query-fdsets: Return information describing all fd sets Note: These commands are not compatible with the existing getfd and closefd QMP commands. Signed-off-by: Corey Bryant <coreyb(a)linux.vnet.ibm.com&gt; --- v5: -This patch is new in v5 and replaces the pass-fd QMP command from v4. -By grouping fds in fd sets, we ease managability with an fd set per file, addressing concerns raised in v4 about handling "reopens" and preventing fd leakage. (eblake(a)redhat.com, kwolf(a)redhat.com, dberrange(a)redhat.com) v6 -Make @fd optional for remove-fd (eblake(a)redhat.com) -Make @fdset-id optional for add-fd (eblake(a)redhat.com) v7: -Share fd sets among all monitor connections (kwolf(a)redhat.com) -Added mon_refcount to keep track of monitor connection count. v8: -Add opaque string to add-fd/query-fdsets. (stefanha(a)linux.vnet.ibm.com) -Use camel case for structures. (stefanha(a)linux.vnet.ibm.com) -Don't return in-use and refcount from query-fdsets. (stefanha(a)linux.vnet.ibm.com) -Don't return removed fd's from query-fdsets. (stefanha(a)linux.vnet.ibm.com) -Use fdset-id rather than fdset_id. (eblake(a)redhat.com) -Fix fd leak in qmp_add_fd(). (stefanha(a)linux.vnet.ibm.com) -Update QMP errors. (stefanha(a)linux.vnet.ibm.com, eblake(a)redhat.com) monitor.c | 188 ++++++++++++++++++++++++++++++++++++++++++++++++++++++ qapi-schema.json | 98 ++++++++++++++++++++++++++++ qmp-commands.hx | 117 +++++++++++++++++++++++++++++++++ 3 files changed, 403 insertions(+) diff --git a/monitor.c b/monitor.c index 49dccfe..f9a0577 100644 --- a/monitor.c +++ b/monitor.c @@ -140,6 +140,24 @@ struct mon_fd_t { QLIST_ENTRY(mon_fd_t) next; }; +/* file descriptor associated with a file descriptor set */ +typedef struct MonFdsetFd MonFdsetFd; +struct MonFdsetFd { + int fd; + bool removed; + char *opaque; + QLIST_ENTRY(MonFdsetFd) next; +}; + +/* file descriptor set containing fds passed via SCM_RIGHTS */ +typedef struct MonFdset MonFdset; +struct MonFdset { + int64_t id; + int refcount; + QLIST_HEAD(, MonFdsetFd) fds; + QLIST_ENTRY(MonFdset) next; +}; + typedef struct MonitorControl { QObject *id; JSONMessageParser parser; @@ -211,6 +229,8 @@ static inline int mon_print_count_get(const Monitor *mon) { return 0; } #define QMP_ACCEPT_UNKNOWNS 1 static QLIST_HEAD(mon_list, Monitor) mon_list; +static QLIST_HEAD(mon_fdsets, MonFdset) mon_fdsets; +static int mon_refcount;