Signed-off-by: Ronald G. Minnich <rminnich@xxxxxxxxx>
Signed-off-by: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
---
Documentation/lguest/lguest.c | 61 +++++++++++++++++++++--------------------
1 file changed, 32 insertions(+), 29 deletions(-)
===================================================================
--- a/Documentation/lguest/lguest.c
+++ b/Documentation/lguest/lguest.c
@@ -15,6 +15,7 @@
#include <stdlib.h>
#include <elf.h>
#include <sys/mman.h>
+#include <sys/param.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/wait.h>
@@ -162,6 +163,30 @@ static unsigned long entry_point(void *s
errx(1, "Is this image a genuine lguest?");
}
+/* This routine is used to load the kernel or initrd. It tries mmap, but if
+ * that fails (Plan 9's kernel file isn't nicely aligned on page boundaries),
+ * it falls back to reading the memory in. */
+static void map_at(int fd, void *addr, unsigned long offset, unsigned long len)
+{
+ ssize_t r;
+
+ /* We map writable even though for some segments are marked read-only.
+ * The kernel really wants to be writable: it patches its own
+ * instructions.
+ *
+ * MAP_PRIVATE means that the page won't be copied until a write is
+ * done to it. This allows us to share untouched memory between
+ * Guests. */
+ if (mmap(addr, len, PROT_READ|PROT_WRITE|PROT_EXEC,
+ MAP_FIXED|MAP_PRIVATE, fd, offset) != MAP_FAILED)
+ return;
+
+ /* pread does a seek and a read in one shot: saves a few lines. */
+ r = pread(fd, addr, len, offset);
+ if (r != len)
+ err(1, "Reading offset %lu len %lu gave %zi", offset, len, r);
+}
+
/* This routine takes an open vmlinux image, which is in ELF, and maps it into
* the Guest memory. ELF = Embedded Linking Format, which is the format used
* by all modern binaries on Linux including the kernel.
@@ -176,7 +201,6 @@ static unsigned long map_elf(int elf_fd,
static unsigned long map_elf(int elf_fd, const Elf32_Ehdr *ehdr,
unsigned long *page_offset)
{
- void *addr;
Elf32_Phdr phdr[ehdr->e_phnum];
unsigned int i;
unsigned long start = -1UL, end = 0;
@@ -227,23 +251,9 @@ static unsigned long map_elf(int elf_fd,
if (phdr[i].p_paddr + phdr[i].p_filesz > end)
end = phdr[i].p_paddr + phdr[i].p_filesz;
- /* We map this section of the file at its physical address. We
- * map it read & write even if the header says this segment is
- * read-only. The kernel really wants to be writable: it
- * patches its own instructions which would normally be
- * read-only.
- *
- * MAP_PRIVATE means that the page won't be copied until a
- * write is done to it. This allows us to share much of the
- * kernel memory between Guests. */
- addr = mmap((void *)phdr[i].p_paddr,
- phdr[i].p_filesz,
- PROT_READ|PROT_WRITE|PROT_EXEC,
- MAP_FIXED|MAP_PRIVATE,
- elf_fd, phdr[i].p_offset);
- if (addr != (void *)phdr[i].p_paddr)
- err(1, "Mmaping vmlinux seg %i gave %p not %p",
- i, addr, (void *)phdr[i].p_paddr);
+ /* We map this section of the file at its physical address. */
+ map_at(elf_fd, (void *)phdr[i].p_paddr,
+ phdr[i].p_offset, phdr[i].p_filesz);
}
return entry_point((void *)start, (void *)end, *page_offset);
@@ -402,27 +412,20 @@ static unsigned long load_initrd(const c
int ifd;
struct stat st;
unsigned long len;
- void *iaddr;
ifd = open_or_die(name, O_RDONLY);
/* fstat() is needed to get the file size. */
if (fstat(ifd, &st) < 0)
err(1, "fstat() on initrd '%s'", name);
- /* The length needs to be rounded up to a page size: mmap needs the
- * address to be page aligned. */
+ /* We map the initrd at the top of memory, but mmap wants it to be
+ * page-aligned, so we round the size up for that. */
len = page_align(st.st_size);
- /* We map the initrd at the top of memory. */
- iaddr = mmap((void *)mem - len, st.st_size,
- PROT_READ|PROT_EXEC|PROT_WRITE,
- MAP_FIXED|MAP_PRIVATE, ifd, 0);
- if (iaddr != (void *)mem - len)
- err(1, "Mmaping initrd '%s' returned %p not %p",
- name, iaddr, (void *)mem - len);
+ map_at(ifd, (void *)mem - len, 0, st.st_size);
/* Once a file is mapped, you can close the file descriptor. It's a
* little odd, but quite useful. */
close(ifd);
- verbose("mapped initrd %s size=%lu @ %p\n", name, st.st_size, iaddr);
+ verbose("mapped initrd %s size=%lu @ %p\n", name, len, (void*)mem-len);
/* We return the initrd size. */
return len;
--
there are those who do and those who hang on and you don't see too
many doers quoting their contemporaries. -- Larry McVoy
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