[v6,01/19] linux-user: Introduce imgsrc_read, imgsrc_read_alloc

diff --git a/linux-user/loader.h b/linux-user/loader.h
index 324e5c872a..da6591fff0 100644
--- a/linux-user/loader.h
+++ b/linux-user/loader.h
@@ -18,6 +18,48 @@ 
 #ifndef LINUX_USER_LOADER_H
 #define LINUX_USER_LOADER_H
 
+typedef struct {
+    const void *cache;
+    unsigned int cache_size;
+    int fd;
+} ImageSource;
+
+/**
+ * imgsrc_read: Read from ImageSource
+ * @dst: destination for read
+ * @offset: offset within file for read
+ * @len: size of the read
+ * @img: ImageSource to read from
+ * @errp: Error details.
+ *
+ * Read into @dst, using the cache when possible.
+ */
+bool imgsrc_read(void *dst, off_t offset, size_t len,
+                 const ImageSource *img, Error **errp);
+
+/**
+ * imgsrc_read_alloc: Read from ImageSource
+ * @offset: offset within file for read
+ * @size: size of the read
+ * @img: ImageSource to read from
+ * @errp: Error details.
+ *
+ * Read into newly allocated memory, using the cache when possible.
+ */
+void *imgsrc_read_alloc(off_t offset, size_t len,
+                        const ImageSource *img, Error **errp);
+
+/**
+ * imgsrc_mmap: Map from ImageSource
+ *
+ * If @src has a file descriptor, pass on to target_mmap.  Otherwise,
+ * this is "mapping" from a host buffer, which resolves to memcpy.
+ * Therefore, flags must be MAP_PRIVATE | MAP_FIXED; the argument is
+ * retained for clarity.
+ */
+abi_long imgsrc_mmap(abi_ulong start, abi_ulong len, int prot,
+                     int flags, const ImageSource *src, abi_ulong offset);
+
 /*
  * Read a good amount of data initially, to hopefully get all the
  * program headers loaded.
@@ -29,15 +71,16 @@ 
  * used when loading binaries.
  */
 struct linux_binprm {
-        char buf[BPRM_BUF_SIZE] __attribute__((aligned));
-        abi_ulong p;
-        int fd;
-        int e_uid, e_gid;
-        int argc, envc;
-        char **argv;
-        char **envp;
-        char *filename;        /* Name of binary */
-        int (*core_dump)(int, const CPUArchState *); /* coredump routine */
+    char buf[BPRM_BUF_SIZE] __attribute__((aligned));
+    ImageSource src;
+    abi_ulong p;
+    int fd;
+    int e_uid, e_gid;
+    int argc, envc;
+    char **argv;
+    char **envp;
+    char *filename;        /* Name of binary */
+    int (*core_dump)(int, const CPUArchState *); /* coredump routine */
 };
 
 void do_init_thread(struct target_pt_regs *regs, struct image_info *infop);
diff --git a/linux-user/linuxload.c b/linux-user/linuxload.c
index 745cce70ab..3536dd8104 100644
--- a/linux-user/linuxload.c
+++ b/linux-user/linuxload.c
@@ -3,7 +3,9 @@ 
 #include "qemu/osdep.h"
 #include "qemu.h"
 #include "user-internals.h"
+#include "user-mmap.h"
 #include "loader.h"
+#include "qapi/error.h"
 
 #define NGROUPS 32
 
@@ -76,6 +78,10 @@  static int prepare_binprm(struct linux_binprm *bprm)
         /* Make sure the rest of the loader won't read garbage.  */
         memset(bprm->buf + retval, 0, BPRM_BUF_SIZE - retval);
     }
+
+    bprm->src.cache = bprm->buf;
+    bprm->src.cache_size = retval;
+
     return retval;
 }
 
@@ -139,6 +145,7 @@  int loader_exec(int fdexec, const char *filename, char **argv, char **envp,
     int retval;
 
     bprm->fd = fdexec;
+    bprm->src.fd = fdexec;
     bprm->filename = (char *)filename;
     bprm->argc = count(argv);
     bprm->argv = argv;
@@ -173,3 +180,86 @@  int loader_exec(int fdexec, const char *filename, char **argv, char **envp,
 
     return retval;
 }
+
+bool imgsrc_read(void *dst, off_t offset, size_t len,
+                 const ImageSource *img, Error **errp)
+{
+    ssize_t ret;
+
+    if (offset + len <= img->cache_size) {
+        memcpy(dst, img->cache + offset, len);
+        return true;
+    }
+
+    if (img->fd < 0) {
+        error_setg(errp, "read past end of buffer");
+        return false;
+    }
+
+    ret = pread(img->fd, dst, len, offset);
+    if (ret == len) {
+        return true;
+    }
+    if (ret < 0) {
+        error_setg_errno(errp, errno, "Error reading file header");
+    } else {
+        error_setg(errp, "Incomplete read of file header");
+    }
+    return false;
+}
+
+void *imgsrc_read_alloc(off_t offset, size_t len,
+                        const ImageSource *img, Error **errp)
+{
+    void *alloc = g_malloc(len);
+    bool ok = imgsrc_read(alloc, offset, len, img, errp);
+
+    if (!ok) {
+        g_free(alloc);
+        alloc = NULL;
+    }
+    return alloc;
+}
+
+abi_long imgsrc_mmap(abi_ulong start, abi_ulong len, int prot,
+                     int flags, const ImageSource *src, abi_ulong offset)
+{
+    const int prot_write = PROT_READ | PROT_WRITE;
+    abi_long ret;
+    void *haddr;
+
+    assert(flags == (MAP_PRIVATE | MAP_FIXED));
+
+    if (src->fd >= 0) {
+        return target_mmap(start, len, prot, flags, src->fd, offset);
+    }
+
+    /*
+     * This case is for the vdso; we don't expect bad images.
+     * The mmap may extend beyond the end of the image, especially
+     * to the end of the page.  Zero fill.
+     */
+    assert(offset < src->cache_size);
+
+    ret = target_mmap(start, len, prot_write, flags | MAP_ANON, -1, 0);
+    if (ret == -1) {
+        return ret;
+    }
+
+    haddr = lock_user(VERIFY_WRITE, start, len, 0);
+    assert(haddr != NULL);
+    if (offset + len <= src->cache_size) {
+        memcpy(haddr, src->cache + offset, len);
+    } else {
+        size_t rest = src->cache_size - offset;
+        memcpy(haddr, src->cache + offset, rest);
+        memset(haddr + rest, 0, len - rest);
+    }
+    unlock_user(haddr, start, len);
+
+    if (prot != prot_write) {
+        target_mprotect(start, len, prot);
+    }
+
+    return ret;
+}