[v3] memory-backend-file related improvements and VM templating support

[PATCH v3 07/11] softmmu/physmem: Never return directories from file_ram_open()

David Hildenbrand posted 11 patches 1 year, 3 months ago

Diff against v2 v4
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Maintainers: David Hildenbrand <david@redhat.com>, Igor Mammedov <imammedo@redhat.com>, Elena Ufimtseva <elena.ufimtseva@oracle.com>, Jagannathan Raman <jag.raman@oracle.com>, "Michael S. Tsirkin" <mst@redhat.com>, Ani Sinha <anisinha@redhat.com>, Eduardo Habkost <eduardo@habkost.net>, Marcel Apfelbaum <marcel.apfelbaum@gmail.com>, "Philippe Mathieu-Daudé" <philmd@linaro.org>, Yanan Wang <wangyanan55@huawei.com>, Xiao Guangrong <xiaoguangrong.eric@gmail.com>, Daniel Henrique Barboza <danielhb413@gmail.com>, "Cédric Le Goater" <clg@kaod.org>, David Gibson <david@gibson.dropbear.id.au>, Greg Kurz <groug@kaod.org>, Harsh Prateek Bora <harshpb@linux.ibm.com>, Paolo Bonzini <pbonzini@redhat.com>, Peter Xu <peterx@redhat.com>, "Daniel P. Berrangé" <berrange@redhat.com>, Eric Blake <eblake@redhat.com>, Markus Armbruster <armbru@redhat.com>

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[PATCH v3 07/11] softmmu/physmem: Never return directories from file_ram_open()

Posted by David Hildenbrand 1 year, 3 months ago

open() does not fail on directories when opening them readonly (O_RDONLY).

Currently, we succeed opening such directories and fail later during
mmap(), resulting in a misleading error message.

$ ./qemu-system-x86_64 \
    -object memory-backend-file,id=ram0,mem-path=tmp,readonly=true,size=1g
 qemu-system-x86_64: unable to map backing store for guest RAM: No such device

To identify directories and handle them accordingly in file_ram_open()
also when readonly=true was specified, detect if we just opened a directory
using fstat() instead. Then, fail file_ram_open() right away, similarly
to how we now fail if the file does not exist and we want to open the
file readonly.

With this change, we get a nicer error message:
 qemu-system-x86_64: can't open backing store tmp for guest RAM: Is a directory

Note that the only memory-backend-file will end up calling
memory_region_init_ram_from_file() -> qemu_ram_alloc_from_file() ->
file_ram_open().

Reported-by: Thiner Logoer <logoerthiner1@163.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
---
 softmmu/physmem.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/softmmu/physmem.c b/softmmu/physmem.c
index f8c47ecb85..2d903e479b 100644
--- a/softmmu/physmem.c
+++ b/softmmu/physmem.c
@@ -1300,6 +1300,25 @@ static int file_ram_open(const char *path,
     for (;;) {
         fd = open(path, readonly ? O_RDONLY : O_RDWR);
         if (fd >= 0) {
+            /*
+             * open(O_RDONLY) won't fail with EISDIR. Check manually if we
+             * opened a directory and fail similarly to how we fail ENOENT
+             * in readonly mode. Note that mkstemp() would imply O_RDWR.
+             */
+            if (readonly) {
+                struct stat file_stat;
+
+                if (fstat(fd, &file_stat)) {
+                    close(fd);
+                    if (errno == EINTR) {
+                        continue;
+                    }
+                    return -errno;
+                } else if (S_ISDIR(file_stat.st_mode)) {
+                    close(fd);
+                    return -EISDIR;
+                }
+            }
             /* @path names an existing file, use it */
             break;
         }
-- 
2.41.0

Re: [PATCH v3 07/11] softmmu/physmem: Never return directories from file_ram_open()

Posted by Peter Xu 1 year, 3 months ago

On Wed, Aug 23, 2023 at 05:34:07PM +0200, David Hildenbrand wrote:
> open() does not fail on directories when opening them readonly (O_RDONLY).
> 
> Currently, we succeed opening such directories and fail later during
> mmap(), resulting in a misleading error message.
> 
> $ ./qemu-system-x86_64 \
>     -object memory-backend-file,id=ram0,mem-path=tmp,readonly=true,size=1g
>  qemu-system-x86_64: unable to map backing store for guest RAM: No such device
> 
> To identify directories and handle them accordingly in file_ram_open()
> also when readonly=true was specified, detect if we just opened a directory
> using fstat() instead. Then, fail file_ram_open() right away, similarly
> to how we now fail if the file does not exist and we want to open the
> file readonly.
> 
> With this change, we get a nicer error message:
>  qemu-system-x86_64: can't open backing store tmp for guest RAM: Is a directory
> 
> Note that the only memory-backend-file will end up calling
> memory_region_init_ram_from_file() -> qemu_ram_alloc_from_file() ->
> file_ram_open().
> 
> Reported-by: Thiner Logoer <logoerthiner1@163.com>
> Signed-off-by: David Hildenbrand <david@redhat.com>

Reviewed-by: Peter Xu <peterx@redhat.com>

-- 
Peter Xu