[Qemu-devel] Using directory as initrd

[Kasper Dupont <kasperd@fjtcb.17.jan.2016.kasperd.net>]

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I would like to use a directory as initrd file without
having to write it to an initrd file each time I have
changed anything in that directory.

I have written code to pipe an initrd directly from cpio
to qemu. Do you have any feedback on the attached patch?

-- 
Kasper Dupont -- Rigtige mænd skriver deres egne backupprogrammer
#define _(_)"d.%.4s%."_"2s" /* This is my email address */
char*_="@2kaspner"_()"%03"_("4s%.")"t\n";printf(_+11,_+6,_,12,_+2,_+7,_+6);

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diff -up qemu-2.0.0+dfsg/hw/core/loader.c.orig qemu-2.0.0+dfsg/hw/core/loader.c
--- qemu-2.0.0+dfsg/hw/core/loader.c.orig	2014-04-17 15:30:59.000000000 +0200
+++ qemu-2.0.0+dfsg/hw/core/loader.c	2016-01-17 19:38:01.505138214 +0100
@@ -137,6 +137,70 @@ void pstrcpy_targphys(const char *name,
     }
 }
 
+/* return the size or -1 if error */
+int load_initrd(const char *filename, uint8_t **addr)
+{
+    pid_t child = 0;
+    int fd, size = 0, buffer_size = 4096;
+    fd = open(filename, O_RDONLY | O_BINARY);
+    if (fd < 0)
+        return -1;
+
+    *addr = malloc(buffer_size);
+
+    while(*addr) {
+        int bytes_read = read(fd, (*addr) + size, buffer_size - size);
+
+        if (bytes_read == 0) {
+            close(fd);
+            if (child) {
+                waitpid(child, NULL, 0);
+            }
+            return size;
+        }
+
+        if (bytes_read > 0) {
+            size += bytes_read;
+        } else {
+            int pipefd[2];
+
+            if (errno != EISDIR)
+                return -1;
+
+            assert(!child);
+
+            if (pipe(pipefd))
+                return -1;
+
+            child = fork();
+            if (child == -1)
+                return -1;
+
+            if (!child) {
+                if(fchdir(fd))
+                    error(1, errno, "fchdir failed");
+                if(dup2(pipefd[1], 1) == -1)
+                    error(1, errno, "dup2 failed");
+                execlp("/bin/sh", "/bin/sh", "-c",
+                       "find . | cpio --quiet -R 0:0 -o -H newc",
+                       NULL);
+                error(1, errno, "/bin/sh");
+            }
+
+            close(fd);
+            close(pipefd[1]);
+            fd = pipefd[0];
+        }
+
+        if (size == buffer_size) {
+            buffer_size <<= 1;
+            *addr = realloc(*addr, buffer_size);
+        }
+    }
+
+    return -1;
+}
+
 /* A.OUT loader */
 
 struct exec
diff -up qemu-2.0.0+dfsg/hw/i386/pc.c.orig qemu-2.0.0+dfsg/hw/i386/pc.c
--- qemu-2.0.0+dfsg/hw/i386/pc.c.orig	2014-04-17 15:30:59.000000000 +0200
+++ qemu-2.0.0+dfsg/hw/i386/pc.c	2016-01-17 19:16:04.704258817 +0100
@@ -829,12 +829,13 @@ static void load_linux(FWCfgState *fw_cf
 
     /* load initrd */
     if (initrd_filename) {
+        uint8_t *initrd_load_buffer;
         if (protocol < 0x200) {
             fprintf(stderr, "qemu: linux kernel too old to load a ram disk\n");
             exit(1);
         }
 
-        initrd_size = get_image_size(initrd_filename);
+        initrd_size = load_initrd(initrd_filename, &initrd_load_buffer);
         if (initrd_size < 0) {
             fprintf(stderr, "qemu: error reading initrd %s: %s\n",
                     initrd_filename, strerror(errno));
@@ -844,7 +845,8 @@ static void load_linux(FWCfgState *fw_cf
         initrd_addr = (initrd_max-initrd_size) & ~4095;
 
         initrd_data = g_malloc(initrd_size);
-        load_image(initrd_filename, initrd_data);
+        memcpy(initrd_data, initrd_load_buffer, initrd_size);
+        free(initrd_load_buffer);
 
         fw_cfg_add_i32(fw_cfg, FW_CFG_INITRD_ADDR, initrd_addr);
         fw_cfg_add_i32(fw_cfg, FW_CFG_INITRD_SIZE, initrd_size);
diff -up qemu-2.0.0+dfsg/include/hw/loader.h.orig qemu-2.0.0+dfsg/include/hw/loader.h
--- qemu-2.0.0+dfsg/include/hw/loader.h.orig	2014-04-17 15:30:59.000000000 +0200
+++ qemu-2.0.0+dfsg/include/hw/loader.h	2016-01-17 19:15:30.688236909 +0100
@@ -13,6 +13,7 @@
  */
 int get_image_size(const char *filename);
 int load_image(const char *filename, uint8_t *addr); /* deprecated */
+int load_initrd(const char *filename, uint8_t **addr);
 int load_image_targphys(const char *filename, hwaddr,
                         uint64_t max_sz);