[Qemu-devel] [RFC PATCH 3/4] block: Enable QEMU to retrieve passed fd before attempting open

[Corey Bryant <coreyb@linux.vnet.ibm.com>]

With this patch, when QEMU needs to "open" a file, it will first
check to see if a matching filename/fd pair were passed via the
-filefd command line option or the getfd_file monitor command.
If a match is found, QEMU will use the passed fd and will not
attempt to open the file.  Otherwise, if a match is not found,
QEMU will attempt to open the file on it's own.

Signed-off-by: Corey Bryant <coreyb@linux.vnet.ibm.com>
---
 block.c           |   31 +++++++++++++++++++++++++++++++
 block/raw-posix.c |   20 ++++++++++----------
 block/raw-win32.c |    4 ++--
 block/vdi.c       |    4 ++--
 block/vmdk.c      |   21 +++++++++------------
 block/vpc.c       |    2 +-
 block/vvfat.c     |    4 ++--
 block_int.h       |   12 ++++++++++++
 vl.c              |    6 ++++++
 9 files changed, 75 insertions(+), 29 deletions(-)

diff --git a/block.c b/block.c
index af2ab4f..6472114 100644
--- a/block.c
+++ b/block.c
@@ -102,6 +102,37 @@ static BlockDriverState *bs_snapshots;
 /* If non-zero, use only whitelisted block drivers */
 static int use_bdrv_whitelist;
 
+static int filename_match(QemuOpts *opts, void *opaque)
+{
+    const char *file = qemu_opt_get(opts, "file");
+    int fd = qemu_opt_get_number(opts, "fd", -1);
+
+    return (strcmp((char *)opaque, file) == 0) ? fd : 0;
+}
+
+int file_open(const char *filename, int flags, mode_t mode)
+{
+    int fd;
+
+#ifdef _WIN32
+    return qemu_open(filename, flags, mode);
+#else
+
+    fd = qemu_opts_foreach(qemu_find_opts("filefd"), filename_match,
+                           (void *)filename, 1);
+    if (fd != 0) {
+        return dup(fd);
+    }
+
+    fd = qemu_get_fd_file(filename, false);
+    if (fd != -1) {
+        return dup(fd);
+    }
+
+    return qemu_open(filename, flags, mode);
+#endif
+}
+
 #ifdef _WIN32
 static int is_windows_drive_prefix(const char *filename)
 {
diff --git a/block/raw-posix.c b/block/raw-posix.c
index 03fcfcc..4f7b40f 100644
--- a/block/raw-posix.c
+++ b/block/raw-posix.c
@@ -208,7 +208,7 @@ static int raw_open_common(BlockDriverState *bs, const char *filename,
         s->open_flags |= O_DSYNC;
 
     s->fd = -1;
-    fd = qemu_open(filename, s->open_flags, 0644);
+    fd = file_open(filename, s->open_flags, 0644);
     if (fd < 0) {
         ret = -errno;
         if (ret == -EROFS)
@@ -568,8 +568,8 @@ static int raw_create(const char *filename, QEMUOptionParameter *options)
         options++;
     }
 
-    fd = open(filename, O_WRONLY | O_CREAT | O_TRUNC | O_BINARY,
-              0644);
+    fd = file_open(filename, O_WRONLY | O_CREAT | O_TRUNC | O_BINARY,
+                   0644);
     if (fd < 0) {
         result = -errno;
     } else {
@@ -741,7 +741,7 @@ static int hdev_open(BlockDriverState *bs, const char *filename, int flags)
         if ( bsdPath[ 0 ] != '\0' ) {
             strcat(bsdPath,"s0");
             /* some CDs don't have a partition 0 */
-            fd = open(bsdPath, O_RDONLY | O_BINARY | O_LARGEFILE);
+            fd = file_open(bsdPath, O_RDONLY | O_BINARY | O_LARGEFILE, 0);
             if (fd < 0) {
                 bsdPath[strlen(bsdPath)-1] = '1';
             } else {
@@ -798,7 +798,7 @@ static int fd_open(BlockDriverState *bs)
 #endif
             return -EIO;
         }
-        s->fd = open(bs->filename, s->open_flags & ~O_NONBLOCK);
+        s->fd = file_open(bs->filename, s->open_flags & ~O_NONBLOCK, 0);
         if (s->fd < 0) {
             s->fd_error_time = get_clock();
             s->fd_got_error = 1;
@@ -872,7 +872,7 @@ static int hdev_create(const char *filename, QEMUOptionParameter *options)
         options++;
     }
 
-    fd = open(filename, O_WRONLY | O_BINARY);
+    fd = file_open(filename, O_WRONLY | O_BINARY, 0);
     if (fd < 0)
         return -errno;
 
@@ -950,7 +950,7 @@ static int floppy_probe_device(const char *filename)
     if (strstart(filename, "/dev/fd", NULL))
         prio = 50;
 
-    fd = open(filename, O_RDONLY | O_NONBLOCK);
+    fd = file_open(filename, O_RDONLY | O_NONBLOCK, 0);
     if (fd < 0) {
         goto out;
     }
@@ -1003,7 +1003,7 @@ static void floppy_eject(BlockDriverState *bs, bool eject_flag)
         close(s->fd);
         s->fd = -1;
     }
-    fd = open(bs->filename, s->open_flags | O_NONBLOCK);
+    fd = file_open(bs->filename, s->open_flags | O_NONBLOCK, 0);
     if (fd >= 0) {
         if (ioctl(fd, FDEJECT, 0) < 0)
             perror("FDEJECT");
@@ -1053,7 +1053,7 @@ static int cdrom_probe_device(const char *filename)
     int prio = 0;
     struct stat st;
 
-    fd = open(filename, O_RDONLY | O_NONBLOCK);
+    fd = file_open(filename, O_RDONLY | O_NONBLOCK, 0);
     if (fd < 0) {
         goto out;
     }
@@ -1177,7 +1177,7 @@ static int cdrom_reopen(BlockDriverState *bs)
      */
     if (s->fd >= 0)
         close(s->fd);
-    fd = open(bs->filename, s->open_flags, 0644);
+    fd = file_open(bs->filename, s->open_flags, 0644);
     if (fd < 0) {
         s->fd = -1;
         return -EIO;
diff --git a/block/raw-win32.c b/block/raw-win32.c
index e4b0b75..ec4ac96 100644
--- a/block/raw-win32.c
+++ b/block/raw-win32.c
@@ -255,8 +255,8 @@ static int raw_create(const char *filename, QEMUOptionParameter *options)
         options++;
     }
 
-    fd = open(filename, O_WRONLY | O_CREAT | O_TRUNC | O_BINARY,
-              0644);
+    fd = file_open(filename, O_WRONLY | O_CREAT | O_TRUNC | O_BINARY,
+                   0644);
     if (fd < 0)
         return -EIO;
     set_sparse(fd);
diff --git a/block/vdi.c b/block/vdi.c
index 119d3c7..b3ec9b2 100644
--- a/block/vdi.c
+++ b/block/vdi.c
@@ -648,8 +648,8 @@ static int vdi_create(const char *filename, QEMUOptionParameter *options)
         options++;
     }
 
-    fd = open(filename, O_WRONLY | O_CREAT | O_TRUNC | O_BINARY | O_LARGEFILE,
-              0644);
+    fd = file_open(filename, O_WRONLY | O_CREAT | O_TRUNC | O_BINARY | O_LARGEFILE,
+                   0644);
     if (fd < 0) {
         return -errno;
     }
diff --git a/block/vmdk.c b/block/vmdk.c
index 18e9b4c..bda4c1a 100644
--- a/block/vmdk.c
+++ b/block/vmdk.c
@@ -1161,10 +1161,9 @@ static int vmdk_create_extent(const char *filename, int64_t filesize,
     VMDK4Header header;
     uint32_t tmp, magic, grains, gd_size, gt_size, gt_count;
 
-    fd = open(
-        filename,
-        O_WRONLY | O_CREAT | O_TRUNC | O_BINARY | O_LARGEFILE,
-        0644);
+    fd = file_open(filename,
+                   O_WRONLY | O_CREAT | O_TRUNC | O_BINARY | O_LARGEFILE,
+                   0644);
     if (fd < 0) {
         return -errno;
     }
@@ -1484,15 +1483,13 @@ static int vmdk_create(const char *filename, QEMUOptionParameter *options)
             (flags & BLOCK_FLAG_COMPAT6 ? 6 : 4),
             total_size / (int64_t)(63 * 16 * 512));
     if (split || flat) {
-        fd = open(
-                filename,
-                O_WRONLY | O_CREAT | O_TRUNC | O_BINARY | O_LARGEFILE,
-                0644);
+        fd = file_open(filename,
+                       O_WRONLY | O_CREAT | O_TRUNC | O_BINARY | O_LARGEFILE,
+                       0644);
     } else {
-        fd = open(
-                filename,
-                O_WRONLY | O_BINARY | O_LARGEFILE,
-                0644);
+        fd = file_open(filename,
+                       O_WRONLY | O_BINARY | O_LARGEFILE,
+                       0644);
     }
     if (fd < 0) {
         return -errno;
diff --git a/block/vpc.c b/block/vpc.c
index 5cd13d1..c1efb10 100644
--- a/block/vpc.c
+++ b/block/vpc.c
@@ -678,7 +678,7 @@ static int vpc_create(const char *filename, QEMUOptionParameter *options)
     }
 
     /* Create the file */
-    fd = open(filename, O_WRONLY | O_CREAT | O_TRUNC | O_BINARY, 0644);
+    fd = file_open(filename, O_WRONLY | O_CREAT | O_TRUNC | O_BINARY, 0644);
     if (fd < 0) {
         return -EIO;
     }
diff --git a/block/vvfat.c b/block/vvfat.c
index 2dc9d50..1573d8f 100644
--- a/block/vvfat.c
+++ b/block/vvfat.c
@@ -1156,7 +1156,7 @@ static int open_file(BDRVVVFATState* s,mapping_t* mapping)
     if(!s->current_mapping ||
 	    strcmp(s->current_mapping->path,mapping->path)) {
 	/* open file */
-	int fd = open(mapping->path, O_RDONLY | O_BINARY | O_LARGEFILE);
+	int fd = file_open(mapping->path, O_RDONLY | O_BINARY | O_LARGEFILE, 0);
 	if(fd<0)
 	    return -1;
 	vvfat_close_current_file(s);
@@ -2215,7 +2215,7 @@ static int commit_one_file(BDRVVVFATState* s,
     for (i = s->cluster_size; i < offset; i += s->cluster_size)
 	c = modified_fat_get(s, c);
 
-    fd = open(mapping->path, O_RDWR | O_CREAT | O_BINARY, 0666);
+    fd = file_open(mapping->path, O_RDWR | O_CREAT | O_BINARY, 0666);
     if (fd < 0) {
 	fprintf(stderr, "Could not open %s... (%s, %d)\n", mapping->path,
 		strerror(errno), errno);
diff --git a/block_int.h b/block_int.h
index b80e66d..f3b6144 100644
--- a/block_int.h
+++ b/block_int.h
@@ -453,4 +453,16 @@ void stream_start(BlockDriverState *bs, BlockDriverState *base,
                   BlockDriverCompletionFunc *cb,
                   void *opaque, Error **errp);
 
+/**
+ * file_open:
+ * @filename: the filename to attempt to open
+ * @flags: O_ flags that determine how the file is open
+ * @mode: the mode to create the file with if #O_CREAT is included in @flags
+ *
+ * This function behaves just like the @open libc function.  It may, however,
+ * get the file descriptor from the QEMU command line or monitor if QEMU is
+ * being run with fewer privileges.
+ */
+int file_open(const char *filename, int flags, mode_t mode);
+
 #endif /* BLOCK_INT_H */
diff --git a/vl.c b/vl.c
index 23ab3a3..6a55166 100644
--- a/vl.c
+++ b/vl.c
@@ -3201,6 +3201,12 @@ int main(int argc, char **argv, char **envp)
             case QEMU_OPTION_qtest_log:
                 qtest_log = optarg;
                 break;
+            case QEMU_OPTION_filefd:
+                opts = qemu_opts_parse(qemu_find_opts("filefd"), optarg, 0);
+                if (!opts) {
+                    exit(1);
+                }
+                break;
             default:
                 os_parse_cmd_args(popt->index, optarg);
             }
-- 
1.7.7.6