Explain possible reason of an error in scripts that rely on /proc/kallsyms (fixes #1391)

tools/btrfsdist.py

@@ -175,6 +175,7 @@ with open(kallsyms) as syms:
             break
     if ops == '':
         print("ERROR: no btrfs_file_operations in /proc/kallsyms. Exiting.")
+        print("HINT: the kernel should be built with CONFIG_KALLSYMS_ALL.")
         exit()
     bpf_text = bpf_text.replace('BTRFS_FILE_OPERATIONS', ops)
 bpf_text = bpf_text.replace('FACTOR', str(factor))

tools/btrfsslower.py

@@ -268,6 +268,7 @@ with open(kallsyms) as syms:
             break
     if ops == '':
         print("ERROR: no btrfs_file_operations in /proc/kallsyms. Exiting.")
+        print("HINT: the kernel should be built with CONFIG_KALLSYMS_ALL.")
         exit()
     bpf_text = bpf_text.replace('BTRFS_FILE_OPERATIONS', ops)
 if min_ms == 0:

tools/ext4dist.py

@@ -155,6 +155,7 @@ with open(kallsyms) as syms:
             break
     if ops == '':
         print("ERROR: no ext4_file_operations in /proc/kallsyms. Exiting.")
+        print("HINT: the kernel should be built with CONFIG_KALLSYMS_ALL.")
         exit()
     bpf_text = bpf_text.replace('EXT4_FILE_OPERATIONS', ops)
 bpf_text = bpf_text.replace('FACTOR', str(factor))

tools/ext4slower.py

@@ -262,6 +262,7 @@ with open(kallsyms) as syms:
             break
     if ops == '':
         print("ERROR: no ext4_file_operations in /proc/kallsyms. Exiting.")
+        print("HINT: the kernel should be built with CONFIG_KALLSYMS_ALL.")
         exit()
     bpf_text = bpf_text.replace('EXT4_FILE_OPERATIONS', ops)
 if min_ms == 0: