Commit 72d41eb4 authored by Stefan Hajnoczi's avatar Stefan Hajnoczi Committed by Paolo Bonzini
Browse files

memory: fetch pmem size in get_file_size() 



Neither stat(2) nor lseek(2) report the size of Linux devdax pmem
character device nodes.  Commit 314aec4a
("hostmem-file: reject invalid pmem file sizes") added code to
hostmem-file.c to fetch the size from sysfs and compare against the
user-provided size=NUM parameter:

  if (backend->size > size) {
      error_setg(errp, "size property %" PRIu64 " is larger than "
                 "pmem file \"%s\" size %" PRIu64, backend->size,
                 fb->mem_path, size);
      return;
  }

It turns out that exec.c:qemu_ram_alloc_from_fd() already has an
equivalent size check but it skips devdax pmem character devices because
lseek(2) returns 0:

  if (file_size > 0 && file_size < size) {
      error_setg(errp, "backing store %s size 0x%" PRIx64
                 " does not match 'size' option 0x" RAM_ADDR_FMT,
                 mem_path, file_size, size);
      return NULL;
  }

This patch moves the devdax pmem file size code into get_file_size() so
that we check the memory size in a single place:
qemu_ram_alloc_from_fd().  This simplifies the code and makes it more
general.

This also fixes the problem that hostmem-file only checks the devdax
pmem file size when the pmem=on parameter is given.  An unchecked
size=NUM parameter can lead to SIGBUS in QEMU so we must always fetch
the file size for Linux devdax pmem character device nodes.

Signed-off-by: default avatarStefan Hajnoczi <stefanha@redhat.com>
Message-Id: <20190830093056.12572-1-stefanha@redhat.com>
Reviewed-by: default avatarEduardo Habkost <ehabkost@redhat.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 41a26351

backends/hostmem-file.c

+0 −22
Original line number Diff line number Diff line
@@ -58,28 +58,6 @@ file_backend_memory_alloc(HostMemoryBackend *backend, Error **errp) 
        return;

    }



    /*

     * Verify pmem file size since starting a guest with an incorrect size

     * leads to confusing failures inside the guest.

     */

    if (fb->is_pmem) {

        Error *local_err = NULL;

        uint64_t size;



        size = qemu_get_pmem_size(fb->mem_path, &local_err);

        if (local_err) {

            error_propagate(errp, local_err);

            return;

        }



        if (size && backend->size > size) {

            error_setg(errp, "size property %" PRIu64 " is larger than "

                       "pmem file \"%s\" size %" PRIu64, backend->size,

                       fb->mem_path, size);

            return;

        }

    }



    backend->force_prealloc = mem_prealloc;

    name = host_memory_backend_get_name(backend);

    memory_region_init_ram_from_file(&backend->mr, OBJECT(backend),

exec.c

+33 −1
Original line number Diff line number Diff line
@@ -1791,7 +1791,39 @@ long qemu_maxrampagesize(void) 
#ifdef CONFIG_POSIX

static int64_t get_file_size(int fd)

{

    int64_t size = lseek(fd, 0, SEEK_END);

    int64_t size;

#if defined(__linux__)

    struct stat st;



    if (fstat(fd, &st) < 0) {

        return -errno;

    }



    /* Special handling for devdax character devices */

    if (S_ISCHR(st.st_mode)) {

        g_autofree char *subsystem_path = NULL;

        g_autofree char *subsystem = NULL;



        subsystem_path = g_strdup_printf("/sys/dev/char/%d:%d/subsystem",

                                         major(st.st_rdev), minor(st.st_rdev));

        subsystem = g_file_read_link(subsystem_path, NULL);



        if (subsystem && g_str_has_suffix(subsystem, "/dax")) {

            g_autofree char *size_path = NULL;

            g_autofree char *size_str = NULL;



            size_path = g_strdup_printf("/sys/dev/char/%d:%d/size",

                                    major(st.st_rdev), minor(st.st_rdev));



            if (g_file_get_contents(size_path, &size_str, NULL, NULL)) {

                return g_ascii_strtoll(size_str, NULL, 0);

            }

        }

    }

#endif /* defined(__linux__) */



    /* st.st_size may be zero for special files yet lseek(2) works */

    size = lseek(fd, 0, SEEK_END);

    if (size < 0) {

        return -errno;

    }

include/qemu/osdep.h

+0 −13
Original line number Diff line number Diff line
@@ -570,19 +570,6 @@ void qemu_set_tty_echo(int fd, bool echo); 
void os_mem_prealloc(int fd, char *area, size_t sz, int smp_cpus,

                     Error **errp);



/**

 * qemu_get_pmem_size:

 * @filename: path to a pmem file

 * @errp: pointer to a NULL-initialized error object

 *

 * Determine the size of a persistent memory file.  Besides supporting files on

 * DAX file systems, this function also supports Linux devdax character

 * devices.

 *

 * Returns: the size or 0 on failure

 */

uint64_t qemu_get_pmem_size(const char *filename, Error **errp);



/**

 * qemu_get_pid_name:

 * @pid: pid of a process

util/oslib-posix.c

+0 −54
Original line number Diff line number Diff line
@@ -514,60 +514,6 @@ void os_mem_prealloc(int fd, char *area, size_t memory, int smp_cpus, 
    }

}



uint64_t qemu_get_pmem_size(const char *filename, Error **errp)

{

    struct stat st;



    if (stat(filename, &st) < 0) {

        error_setg(errp, "unable to stat pmem file \"%s\"", filename);

        return 0;

    }



#if defined(__linux__)

    /* Special handling for devdax character devices */

    if (S_ISCHR(st.st_mode)) {

        char *subsystem_path = NULL;

        char *subsystem = NULL;

        char *size_path = NULL;

        char *size_str = NULL;

        uint64_t ret = 0;



        subsystem_path = g_strdup_printf("/sys/dev/char/%d:%d/subsystem",

                                         major(st.st_rdev), minor(st.st_rdev));

        subsystem = g_file_read_link(subsystem_path, NULL);

        if (!subsystem) {

            error_setg(errp, "unable to read subsystem for pmem file \"%s\"",

                       filename);

            goto devdax_err;

        }



        if (!g_str_has_suffix(subsystem, "/dax")) {

            error_setg(errp, "pmem file \"%s\" is not a dax device", filename);

            goto devdax_err;

        }



        size_path = g_strdup_printf("/sys/dev/char/%d:%d/size",

                                    major(st.st_rdev), minor(st.st_rdev));

        if (!g_file_get_contents(size_path, &size_str, NULL, NULL)) {

            error_setg(errp, "unable to read size for pmem file \"%s\"",

                       size_path);

            goto devdax_err;

        }



        ret = g_ascii_strtoull(size_str, NULL, 0);



devdax_err:

        g_free(size_str);

        g_free(size_path);

        g_free(subsystem);

        g_free(subsystem_path);

        return ret;

    }

#endif /* defined(__linux__) */



    return st.st_size;

}



char *qemu_get_pid_name(pid_t pid)

{

    char *name = NULL;

util/oslib-win32.c

+0 −6
Original line number Diff line number Diff line
@@ -562,12 +562,6 @@ void os_mem_prealloc(int fd, char *area, size_t memory, int smp_cpus, 
    }

}



uint64_t qemu_get_pmem_size(const char *filename, Error **errp)

{

    error_setg(errp, "pmem support not available");

    return 0;

}



char *qemu_get_pid_name(pid_t pid)

{

    /* XXX Implement me */