Allowed lseekable device files with iso_tree_add_new_cut_out_node(). Proof-of-concept by Ivan Shmakov.

libisofs/fsource.c

@@ -1,5 +1,6 @@
 /*
  * Copyright (c) 2007 Vreixo Formoso
+ * Copyright (c) 2022 Thomas Schmitt
  * 
  * This file is part of the libisofs project; you can redistribute it and/or 
  * modify it under the terms of the GNU General Public License version 2 
@@ -133,3 +134,59 @@ int iso_file_source_get_aa_string(IsoFileSource *src,
     return src->class->get_aa_string(src, aa_string, flag);
 }
 
+
+/* Determine whether src is random-access readable and return its capacity.
+   @flag  bit0= Open and close src
+   @return <0 iso_file_source_lseek failed , >= 0 readable capacity
+*/
+off_t iso_file_source_lseek_capacity(IsoFileSource *src, int flag)
+{
+    int ret, opened = 0;
+    off_t end, old, reset;
+    struct stat info;
+
+    ret = iso_file_source_stat(src, &info);
+    if (ret < 0) {
+        end = -1;
+        goto ex;
+    }
+    if (S_ISDIR(info.st_mode) || S_ISLNK(info.st_mode) || 
+        S_ISFIFO(info.st_mode) || S_ISSOCK(info.st_mode)) {
+        /* open(2) on fifo can block and have side effects.
+           Active Unix sockets have not been tested but they make as few sense
+           as directories or symbolic links.
+        */
+        end = -1;
+        goto ex;
+    }
+
+    if (flag & 1) {
+        ret = iso_file_source_open(src);
+        if (ret < 0) {
+            end = -1;
+            goto ex;
+        }
+        opened = 1;
+    }
+    old = iso_file_source_lseek(src, 0, 1);
+    if (old < 0) {
+        end = -1;
+        goto ex;
+    }
+    end = iso_file_source_lseek(src, 0, 2);
+    if (end < 0) {
+        end = -1;
+        goto ex;
+    }
+    reset = iso_file_source_lseek(src, old, 0);
+    if (reset != old) {
+        end = -1;
+        goto ex;
+    }
+ex:;
+    if (opened) {
+        iso_file_source_close(src);
+    }
+    return end;
+}
+

libisofs/fsource.h

@@ -1,6 +1,6 @@
 /*
  * Copyright (c) 2007 Vreixo Formoso
- * Copyright (c) 2009 - 2016 Thomas Schmitt
+ * Copyright (c) 2009 - 2022 Thomas Schmitt
  * 
  * This file is part of the libisofs project; you can redistribute it and/or 
  * modify it under the terms of the GNU General Public License version 2 
@@ -49,4 +49,10 @@ int iso_ifs_source_clone(IsoFileSource *old_source, IsoFileSource **new_source,
                          int flag);
 
 
+/* Determine whether src is random-access readable and return its capacity.
+   @return -1 iso_file_source_lseek failed , >= 0 readable capacity
+*/
+off_t iso_file_source_lseek_capacity(IsoFileSource *src, int flag);
+
+
 #endif /*LIBISO_FSOURCE_H_*/

libisofs/libisofs.h

@@ -4,7 +4,7 @@
 
 /*
  * Copyright (c) 2007-2008 Vreixo Formoso, Mario Danic
- * Copyright (c) 2009-2021 Thomas Schmitt
+ * Copyright (c) 2009-2022 Thomas Schmitt
  *
  * This file is part of the libisofs project; you can redistribute it and/or
  * modify it under the terms of the GNU General Public License version 2 
@@ -6349,8 +6349,9 @@ int iso_tree_add_new_node(IsoImage *image, IsoDir *parent, const char *name,
  *      according to iso_image_set_truncate_mode().
  *      Its directory path depends on the parent node.
  * @param path
- *      The absolute path of the file in the local filesystem. For now
+ *      The absolute path of the random-access capable file in the local
- *      only regular files and symlinks to regular files are supported.
+ *      filesystem. Only regular files and device files are supported.
+ *      On Linux, only regular files and block device offer random-access.
  * @param offset
  *      Byte number in the given file from where to start reading data.
  * @param size
@@ -6368,8 +6369,11 @@ int iso_tree_add_new_node(IsoImage *image, IsoDir *parent, const char *name,
  *         ISO_NODE_NAME_NOT_UNIQUE, a node with same name already exists
  *         ISO_OUT_OF_MEM
  *         ISO_RR_NAME_TOO_LONG
+ *         ISO_WRONG_ARG_VALUE, if path is not suitable for random access
  *
  * @since 0.6.4
+ *
+ * Device files as path: @since 1.5.6
  */
 int iso_tree_add_new_cut_out_node(IsoImage *image, IsoDir *parent,
                                   const char *name, const char *path,

libisofs/stream.c

@@ -1,6 +1,6 @@
 /*
  * Copyright (c) 2007 Vreixo Formoso
- * Copyright (c) 2009 - 2015 Thomas Schmitt
+ * Copyright (c) 2009 - 2022 Thomas Schmitt
  *
  * This file is part of the libisofs project; you can redistribute it and/or
  * modify it under the terms of the GNU General Public License version 2 
@@ -330,6 +330,7 @@ int cut_out_open(IsoStream *stream)
 {
     int ret;
     struct stat info;
+    off_t src_size, pos;
     IsoFileSource *src;
     struct cut_out_stream *data;
 
@@ -348,20 +349,25 @@ int cut_out_open(IsoStream *stream)
         return ret;
     }
 
-    {
+    if (S_ISREG(info.st_mode)) {
-        off_t ret;
+        src_size= info.st_size;
-        if (data->offset > info.st_size) {
-            /* file is smaller than expected */
-            ret = iso_file_source_lseek(src, info.st_size, 0);
     } else {
-            ret = iso_file_source_lseek(src, data->offset, 0);
+        /* Determine src_size and lseekability of device */
+        src_size = iso_file_source_lseek_capacity(src, 0);
+        if (src_size <= 0)
+            return ISO_WRONG_ARG_VALUE;
     }
-        if (ret < 0) {
+    if (data->offset > src_size) {
-            return (int) ret;
+        /* file is smaller than expected */
+        pos = iso_file_source_lseek(src, src_size, 0);
+    } else {
+        pos = iso_file_source_lseek(src, data->offset, 0);
     }
+    if (pos < 0) {
+        return (int) pos;
     }
     data->pos = 0;
-    if (data->offset + data->size > info.st_size) {
+    if (data->offset + data->size > src_size) {
         return 3; /* file smaller than expected */
     } else {
         return ISO_SUCCESS;
@@ -508,6 +514,7 @@ int iso_cut_out_stream_new(IsoFileSource *src, off_t offset, off_t size,
                            IsoStream **stream)
 {
     int r;
+    off_t src_size;
     struct stat info;
     IsoStream *str;
     struct cut_out_stream *data;
@@ -523,10 +530,16 @@ int iso_cut_out_stream_new(IsoFileSource *src, off_t offset, off_t size,
     if (r < 0) {
         return r;
     }
-    if (!S_ISREG(info.st_mode)) {
+
+    if (S_ISREG(info.st_mode)) {
+        src_size = info.st_size;
+    } else {
+        /* Open src, do iso_source_lseek(SEEK_END), close src */
+        src_size = iso_file_source_lseek_capacity(src, 1);
+        if (src_size <= 0)
             return ISO_WRONG_ARG_VALUE;
     }
-    if (offset > info.st_size) {
+    if (offset > src_size) {
         return ISO_FILE_OFFSET_TOO_BIG;
     }
 
@@ -551,7 +564,7 @@ int iso_cut_out_stream_new(IsoFileSource *src, off_t offset, off_t size,
     iso_file_source_ref(src);
 
     data->offset = offset;
-    data->size = MIN(info.st_size - offset, size);
+    data->size = MIN(src_size - offset, size);
 
     /* get the id numbers */
     data->dev_id = (dev_t) 0;

libisofs/tree.c

@@ -1,6 +1,6 @@
 /*
  * Copyright (c) 2007 Vreixo Formoso
- * Copyright (c) 2011 - 2015 Thomas Schmitt
+ * Copyright (c) 2011 - 2022 Thomas Schmitt
  * 
  * This file is part of the libisofs project; you can redistribute it and/or 
  * modify it under the terms of the GNU General Public License version 2 
@@ -677,6 +677,7 @@ int iso_tree_add_new_cut_out_node(IsoImage *image, IsoDir *parent,
                                   IsoNode **node)
 {
     int result;
+    off_t src_size;
     struct stat info;
     IsoFilesystem *fs;
     IsoFileSource *src;
@@ -715,17 +716,23 @@ int iso_tree_add_new_cut_out_node(IsoImage *image, IsoDir *parent,
         iso_file_source_unref(src);
         return result;
     }
-    if (!S_ISREG(info.st_mode)) {
+
+    if (S_ISREG(info.st_mode)) {
+        src_size = info.st_size;
+    } else {
+        /* Open src, do iso_source_lseek(SEEK_END), close src */
+        src_size = iso_file_source_lseek_capacity(src, 1);
+        if (src_size <= 0)
             return ISO_WRONG_ARG_VALUE;
     }
-    if (offset >= info.st_size) {
+    if (offset >= src_size) {
         return ISO_WRONG_ARG_VALUE;
     }
 
     /* force regular file */
     result = image->builder->create_file(image->builder, image, src, &new);
     
-    /* free the file */
+    /* Give up the newly acquired surplus reference to src */
     iso_file_source_unref(src);
     
     if (result < 0) {