[xen staging] xenstored: use fread() instead of mmap() for reading live update state

[patchbot@xxxxxxx]

commit b29e3a26c29bb8a74bd54308b8a3c7870ea231d9
Author:     Juergen Gross <jgross@xxxxxxxx>
AuthorDate: Thu Jul 31 09:44:07 2025 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Thu Jul 31 09:44:07 2025 +0200

    xenstored: use fread() instead of mmap() for reading live update state
    
    Mini-OS doesn't support using mmap() for accessing a file. In order
    to support reading the live update state from a 9pfs based file, use
    fread() instead of mmap().
    
    While adding the offset member to lu_state, change the type of "size"
    to size_t in order to avoid problems with state exceeding 4GB.
    
    Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
    Reviewed-by: Jason Andryuk <jason.andryuk@xxxxxxx>
---
 tools/xenstored/lu.c | 97 ++++++++++++++++++++++++++++++++--------------------
 1 file changed, 60 insertions(+), 37 deletions(-)

diff --git a/tools/xenstored/lu.c b/tools/xenstored/lu.c
index 77e0d377c5..fa8395eb1e 100644
--- a/tools/xenstored/lu.c
+++ b/tools/xenstored/lu.c
@@ -27,9 +27,11 @@ struct live_update *lu_status;
 
 struct lu_dump_state {
        void *buf;
-       unsigned int size;
-       int fd;
+       unsigned int buf_size;
+       size_t size;
+       size_t offset;
        char *filename;
+       FILE *fp;
 };
 
 static int lu_destroy(void *data)
@@ -80,9 +82,10 @@ bool lu_is_pending(void)
        return lu_status != NULL;
 }
 
-static void lu_get_dump_state(struct lu_dump_state *state)
+static void lu_get_dump_state(void *ctx, struct lu_dump_state *state)
 {
        struct stat statbuf;
+       int fd;
 
        state->size = 0;
 
@@ -91,82 +94,107 @@ static void lu_get_dump_state(struct lu_dump_state *state)
        if (!state->filename)
                barf("Allocation failure");
 
-       state->fd = open(state->filename, O_RDONLY);
-       if (state->fd < 0)
-               return;
-       if (fstat(state->fd, &statbuf) != 0)
-               goto out_close;
+       fd = open(state->filename, O_RDONLY);
+       if (fd < 0)
+               barf("No state file found");
+       if (fstat(fd, &statbuf) != 0)
+               barf("Could not fstat state file");
        state->size = statbuf.st_size;
 
-       state->buf = mmap(NULL, state->size, PROT_READ, MAP_PRIVATE,
-                         state->fd, 0);
-       if (state->buf == MAP_FAILED) {
-               state->size = 0;
-               goto out_close;
-       }
+       /* Start with a 4k buffer. If needed we'll reallocate a larger one. */
+       state->buf_size = 4096;
+       state->buf = talloc_size(ctx, state->buf_size);
+       if (!state->buf)
+               barf("Allocation failure");
 
-       return;
+       state->fp = fdopen(fd, "r");
+}
 
- out_close:
-       close(state->fd);
+static void lu_dump_close(FILE *fp)
+{
+       fclose(fp);
 }
 
 static void lu_close_dump_state(struct lu_dump_state *state)
 {
        assert(state->filename != NULL);
 
-       munmap(state->buf, state->size);
-       close(state->fd);
+       lu_dump_close(state->fp);
 
        unlink(state->filename);
        talloc_free(state->filename);
+       talloc_free(state->buf);
+}
+
+static void lu_read_data(void *ctx, struct lu_dump_state *state,
+                        unsigned int size)
+{
+       if (state->offset + size > state->size)
+               barf("Inconsistent state data");
+
+       if (size > state->buf_size) {
+               state->buf = talloc_realloc_size(ctx, state->buf, size);
+               if (!state->buf)
+                       barf("Allocation failure");
+               state->buf_size = size;
+       }
+
+       if (fread(state->buf, size, 1, state->fp) != 1)
+               barf("State read error");
+
+       state->offset += size;
 }
 
 void lu_read_state(void)
 {
        struct lu_dump_state state = {};
-       struct xs_state_record_header *head;
+       struct xs_state_record_header head;
        void *ctx = talloc_new(NULL); /* Work context for subfunctions. */
        struct xs_state_preamble *pre;
        unsigned int version;
 
        syslog(LOG_INFO, "live-update: read state\n");
-       lu_get_dump_state(&state);
+       lu_get_dump_state(ctx, &state);
        if (state.size == 0)
                barf_perror("No state found after live-update");
 
+       lu_read_data(ctx, &state, sizeof(*pre));
        pre = state.buf;
        version = be32toh(pre->version);
        if (memcmp(pre->ident, XS_STATE_IDENT, sizeof(pre->ident)) ||
            !version || version > XS_STATE_VERSION ||
            pre->flags != XS_STATE_FLAGS)
                barf("Unknown record identifier");
-       for (head = state.buf + sizeof(*pre);
-            head->type != XS_STATE_TYPE_END &&
-               (void *)head - state.buf < state.size;
-            head = (void *)head + sizeof(*head) + head->length) {
-               switch (head->type) {
+
+       for (;;) {
+               lu_read_data(ctx, &state, sizeof(head));
+               head = *(struct xs_state_record_header *)(state.buf);
+               if (head.type == XS_STATE_TYPE_END)
+                       break;
+               lu_read_data(ctx, &state, head.length);
+
+               switch (head.type) {
                case XS_STATE_TYPE_GLOBAL:
-                       read_state_global(ctx, head + 1);
+                       read_state_global(ctx, state.buf);
                        break;
                case XS_STATE_TYPE_CONN:
-                       read_state_connection(ctx, head + 1);
+                       read_state_connection(ctx, state.buf);
                        break;
                case XS_STATE_TYPE_WATCH:
-                       read_state_watch(ctx, head + 1);
+                       read_state_watch(ctx, state.buf);
                        break;
                case XS_STATE_TYPE_TA:
                        xprintf("live-update: ignore transaction record\n");
                        break;
                case XS_STATE_TYPE_NODE:
-                       read_state_node(ctx, head + 1);
+                       read_state_node(ctx, state.buf);
                        break;
                case XS_STATE_TYPE_DOMAIN:
-                       read_state_domain(ctx, head + 1, version);
+                       read_state_domain(ctx, state.buf, version);
                        break;
                default:
                        xprintf("live-update: unknown state record %08x\n",
-                               head->type);
+                               head.type);
                        break;
                }
        }
@@ -271,11 +299,6 @@ static FILE *lu_dump_open(const void *ctx)
        return fdopen(fd, "w");
 }
 
-static void lu_dump_close(FILE *fp)
-{
-       fclose(fp);
-}
-
 static const char *lu_dump_state(const void *ctx, struct connection *conn)
 {
        FILE *fp;
--
generated by git-patchbot for /home/xen/git/xen.git#staging