Create a "qemu_open_err" method which does the same as "qemu_open",
but with a "Error **errp" for error reporting. There should be no
behavioural difference for existing callers at this stage.

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
---
 include/qemu/osdep.h |  1 +
 util/osdep.c         | 71 +++++++++++++++++++++++++++++++++++---------
 2 files changed, 58 insertions(+), 14 deletions(-)

diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h
index 0d26a1b9bd..e41701a308 100644
--- a/include/qemu/osdep.h
+++ b/include/qemu/osdep.h
@@ -483,6 +483,7 @@ int qemu_madvise(void *addr, size_t len, int advice);
 int qemu_mprotect_rwx(void *addr, size_t size);
 int qemu_mprotect_none(void *addr, size_t size);
 
+int qemu_open_err(const char *name, int flags, Error **errp, ...);
 int qemu_open(const char *name, int flags, ...);
 int qemu_close(int fd);
 int qemu_unlink(const char *name);
diff --git a/util/osdep.c b/util/osdep.c
index 4bdbe81cec..450b3a5da3 100644
--- a/util/osdep.c
+++ b/util/osdep.c
@@ -22,6 +22,7 @@
  * THE SOFTWARE.
  */
 #include "qemu/osdep.h"
+#include "qapi/error.h"
 
 /* Needed early for CONFIG_BSD etc. */
 
@@ -282,7 +283,7 @@ int qemu_lock_fd_test(int fd, int64_t start, int64_t len, bool exclusive)
 /*
  * Opens a file with FD_CLOEXEC set
  */
-int qemu_open(const char *name, int flags, ...)
+static int qemu_openv(const char *name, int flags, Error **errp, va_list ap)
 {
     int ret;
     int mode = 0;
@@ -297,24 +298,31 @@ int qemu_open(const char *name, int flags, ...)
 
         fdset_id = qemu_parse_fdset(fdset_id_str);
         if (fdset_id == -1) {
+            error_setg(errp, "Unable to parse fdset %s", name);
             errno = EINVAL;
             return -1;
         }
 
         fd = monitor_fdset_get_fd(fdset_id, flags);
         if (fd < 0) {
+            error_setg_errno(errp, -fd, "Unable acquire FD for %s flags %x",
+                             name, flags);
             errno = -fd;
             return -1;
         }
 
         dupfd = qemu_dup_flags(fd, flags);
         if (dupfd == -1) {
+            error_setg_errno(errp, errno, "Unable dup FD for %s flags %x",
+                             name, flags);
             return -1;
         }
 
         ret = monitor_fdset_dup_fd_add(fdset_id, dupfd);
         if (ret == -1) {
             close(dupfd);
+            error_setg(errp, "Unable save FD for %s flags %x",
+                       name, flags);
             errno = EINVAL;
             return -1;
         }
@@ -324,11 +332,7 @@ int qemu_open(const char *name, int flags, ...)
 #endif
 
     if (flags & O_CREAT) {
-        va_list ap;
-
-        va_start(ap, flags);
         mode = va_arg(ap, int);
-        va_end(ap);
     }
 
 #ifdef O_CLOEXEC
@@ -340,25 +344,64 @@ int qemu_open(const char *name, int flags, ...)
     }
 #endif
 
+    if (ret == -1) {
+        const char *action = "open";
+        if (flags & O_CREAT) {
+            action = "create";
+        }
 #ifdef O_DIRECT
-    if (ret == -1 && errno == EINVAL && (flags & O_DIRECT)) {
-        int newflags = flags & ~O_DIRECT;
+        if (errno == EINVAL && (flags & O_DIRECT)) {
+            int newflags = flags & ~O_DIRECT;
 # ifdef O_CLOEXEC
-        ret = open(name, newflags | O_CLOEXEC, mode);
+            ret = open(name, newflags | O_CLOEXEC, mode);
 # else
-        ret = open(name, newflags, mode);
+            ret = open(name, newflags, mode);
 # endif
-        if (ret != -1) {
-            close(ret);
-            error_report("file system does not support O_DIRECT");
-            errno = EINVAL;
+            if (ret != -1) {
+                close(ret);
+                error_setg(errp, "Unable to %s '%s' flags 0x%x: "
+                           "filesystem does not support O_DIRECT",
+                           action, name, flags);
+                if (!errp) {
+                    error_report("file system does not support O_DIRECT");
+                }
+                errno = EINVAL;
+                return -1;
+            }
         }
-    }
 #endif /* O_DIRECT */
+        error_setg_errno(errp, errno, "Unable to %s '%s' flags 0x%x",
+                         action, name, flags);
+    }
+
 
     return ret;
 }
 
+int qemu_open_err(const char *name, int flags, Error **errp, ...)
+{
+    va_list ap;
+    int rv;
+
+    va_start(ap, errp);
+    rv = qemu_openv(name, flags, errp, ap);
+    va_end(ap);
+
+    return rv;
+}
+
+int qemu_open(const char *name, int flags, ...)
+{
+    va_list ap;
+    int rv;
+
+    va_start(ap, flags);
+    rv = qemu_openv(name, flags, NULL, ap);
+    va_end(ap);
+
+    return rv;
+}
+
 int qemu_close(int fd)
 {
     int64_t fdset_id;
-- 
2.26.2

Daniel P. Berrangé <berrange@redhat.com> writes:

> Create a "qemu_open_err" method which does the same as "qemu_open",
> but with a "Error **errp" for error reporting. There should be no
> behavioural difference for existing callers at this stage.
>
> Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
> ---
>  include/qemu/osdep.h |  1 +
>  util/osdep.c         | 71 +++++++++++++++++++++++++++++++++++---------
>  2 files changed, 58 insertions(+), 14 deletions(-)
>
> diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h
> index 0d26a1b9bd..e41701a308 100644
> --- a/include/qemu/osdep.h
> +++ b/include/qemu/osdep.h
> @@ -483,6 +483,7 @@ int qemu_madvise(void *addr, size_t len, int advice);
>  int qemu_mprotect_rwx(void *addr, size_t size);
>  int qemu_mprotect_none(void *addr, size_t size);
>  
> +int qemu_open_err(const char *name, int flags, Error **errp, ...);
>  int qemu_open(const char *name, int flags, ...);
>  int qemu_close(int fd);
>  int qemu_unlink(const char *name);
> diff --git a/util/osdep.c b/util/osdep.c
> index 4bdbe81cec..450b3a5da3 100644
> --- a/util/osdep.c
> +++ b/util/osdep.c
> @@ -22,6 +22,7 @@
>   * THE SOFTWARE.
>   */
>  #include "qemu/osdep.h"
> +#include "qapi/error.h"
>  
>  /* Needed early for CONFIG_BSD etc. */
>  
> @@ -282,7 +283,7 @@ int qemu_lock_fd_test(int fd, int64_t start, int64_t len, bool exclusive)
>  /*
>   * Opens a file with FD_CLOEXEC set
>   */
> -int qemu_open(const char *name, int flags, ...)
> +static int qemu_openv(const char *name, int flags, Error **errp, va_list ap)
>  {
>      int ret;
>      int mode = 0;
> @@ -297,24 +298,31 @@ int qemu_open(const char *name, int flags, ...)
>  
>          fdset_id = qemu_parse_fdset(fdset_id_str);
>          if (fdset_id == -1) {
> +            error_setg(errp, "Unable to parse fdset %s", name);
>              errno = EINVAL;
>              return -1;
>          }
>  
>          fd = monitor_fdset_get_fd(fdset_id, flags);
>          if (fd < 0) {
> +            error_setg_errno(errp, -fd, "Unable acquire FD for %s flags %x",
> +                             name, flags);
>              errno = -fd;
>              return -1;
>          }
>  
>          dupfd = qemu_dup_flags(fd, flags);
>          if (dupfd == -1) {
> +            error_setg_errno(errp, errno, "Unable dup FD for %s flags %x",
> +                             name, flags);
>              return -1;
>          }
>  
>          ret = monitor_fdset_dup_fd_add(fdset_id, dupfd);
>          if (ret == -1) {
>              close(dupfd);
> +            error_setg(errp, "Unable save FD for %s flags %x",
> +                       name, flags);
>              errno = EINVAL;
>              return -1;
>          }
> @@ -324,11 +332,7 @@ int qemu_open(const char *name, int flags, ...)
>  #endif
>  
>      if (flags & O_CREAT) {
> -        va_list ap;
> -
> -        va_start(ap, flags);
>          mode = va_arg(ap, int);
> -        va_end(ap);
>      }
>  
>  #ifdef O_CLOEXEC
> @@ -340,25 +344,64 @@ int qemu_open(const char *name, int flags, ...)
>      }
>  #endif
>  
> +    if (ret == -1) {
> +        const char *action = "open";
> +        if (flags & O_CREAT) {
> +            action = "create";
> +        }
>  #ifdef O_DIRECT
> -    if (ret == -1 && errno == EINVAL && (flags & O_DIRECT)) {
> -        int newflags = flags & ~O_DIRECT;
> +        if (errno == EINVAL && (flags & O_DIRECT)) {
> +            int newflags = flags & ~O_DIRECT;
>  # ifdef O_CLOEXEC
> -        ret = open(name, newflags | O_CLOEXEC, mode);
> +            ret = open(name, newflags | O_CLOEXEC, mode);
>  # else
> -        ret = open(name, newflags, mode);
> +            ret = open(name, newflags, mode);
>  # endif
> -        if (ret != -1) {
> -            close(ret);
> -            error_report("file system does not support O_DIRECT");
> -            errno = EINVAL;
> +            if (ret != -1) {
> +                close(ret);
> +                error_setg(errp, "Unable to %s '%s' flags 0x%x: "
> +                           "filesystem does not support O_DIRECT",
> +                           action, name, flags);
> +                if (!errp) {

If the caller ignores errors, ...

> +                    error_report("file system does not support O_DIRECT");

... we report this error to stderr (but not any of the other ones).
This is weird.  I figure you do it here to reproduce the weirdness of
qemu_open() before the patch.  Goes back to

    commit a5813077aac7865f69b7ee46a594f3705429f7cd
    Author: Stefan Hajnoczi <stefanha@redhat.com>
    Date:   Thu Aug 22 11:29:03 2013 +0200

        osdep: warn if open(O_DIRECT) on fails with EINVAL

        Print a warning when opening a file O_DIRECT fails with EINVAL.  This
        saves users a lot of time trying to figure out the EINVAL error, which
        is typical when attempting to open a file O_DIRECT on Linux tmpfs.

        Reported-by: Deepak C Shetty <deepakcs@linux.vnet.ibm.com>
        Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
        Reviewed-by: Eric Blake <eblake@redhat.com>

The message isn't phrased as a warning, though.  Should it use
warn_report()?  Stefan?

Regardless, since use of error_report() in a function that returns
errors through its Error ** parameter is an anti-pattern, this use needs
a comment.  I'd make it a TODO comment: convert all callers where the
warning is wanted to qemu_open_err(), then drop it.

> +                }
> +                errno = EINVAL;
> +                return -1;
> +            }
>          }
> -    }
>  #endif /* O_DIRECT */
> +        error_setg_errno(errp, errno, "Unable to %s '%s' flags 0x%x",
> +                         action, name, flags);
> +    }
> +
>  
>      return ret;
>  }
>  
> +int qemu_open_err(const char *name, int flags, Error **errp, ...)
> +{
> +    va_list ap;
> +    int rv;
> +
> +    va_start(ap, errp);
> +    rv = qemu_openv(name, flags, errp, ap);
> +    va_end(ap);
> +
> +    return rv;
> +}
> +
> +int qemu_open(const char *name, int flags, ...)
> +{
> +    va_list ap;
> +    int rv;
> +
> +    va_start(ap, flags);
> +    rv = qemu_openv(name, flags, NULL, ap);
> +    va_end(ap);
> +
> +    return rv;
> +}

I'd rename this to qemu_open_with_bad_error_messages().

For better ones, callers can use

    if (qemu_open_err(name, flags, &err) < 0) {
        error_report_err(err);
        ...
    }

or, where the error is fatal
    
    qemu_open_err(name, flags, &error_fatal);

If you prefer not to rename it now, please add a comment why it should
not be used in new code, and existing uses should be converted.

If you rename, call the new one qemu_open().

> +
>  int qemu_close(int fd)
>  {
>      int64_t fdset_id;

On Thu, Jul 02, 2020 at 07:13:08AM +0200, Markus Armbruster wrote:
> Daniel P. Berrangé <berrange@redhat.com> writes:
> 
> > Create a "qemu_open_err" method which does the same as "qemu_open",
> > but with a "Error **errp" for error reporting. There should be no
> > behavioural difference for existing callers at this stage.
> >
> > Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
> > ---
> >  include/qemu/osdep.h |  1 +
> >  util/osdep.c         | 71 +++++++++++++++++++++++++++++++++++---------
> >  2 files changed, 58 insertions(+), 14 deletions(-)
> >
> > diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h
> > index 0d26a1b9bd..e41701a308 100644
> > --- a/include/qemu/osdep.h
> > +++ b/include/qemu/osdep.h
> > @@ -483,6 +483,7 @@ int qemu_madvise(void *addr, size_t len, int advice);
> >  int qemu_mprotect_rwx(void *addr, size_t size);
> >  int qemu_mprotect_none(void *addr, size_t size);
> >  
> > +int qemu_open_err(const char *name, int flags, Error **errp, ...);
> >  int qemu_open(const char *name, int flags, ...);
> >  int qemu_close(int fd);
> >  int qemu_unlink(const char *name);
> > diff --git a/util/osdep.c b/util/osdep.c
> > index 4bdbe81cec..450b3a5da3 100644
> > --- a/util/osdep.c
> > +++ b/util/osdep.c
> > @@ -22,6 +22,7 @@
> >   * THE SOFTWARE.
> >   */
> >  #include "qemu/osdep.h"
> > +#include "qapi/error.h"
> >  
> >  /* Needed early for CONFIG_BSD etc. */
> >  
> > @@ -282,7 +283,7 @@ int qemu_lock_fd_test(int fd, int64_t start, int64_t len, bool exclusive)
> >  /*
> >   * Opens a file with FD_CLOEXEC set
> >   */
> > -int qemu_open(const char *name, int flags, ...)
> > +static int qemu_openv(const char *name, int flags, Error **errp, va_list ap)
> >  {
> >      int ret;
> >      int mode = 0;
> > @@ -297,24 +298,31 @@ int qemu_open(const char *name, int flags, ...)
> >  
> >          fdset_id = qemu_parse_fdset(fdset_id_str);
> >          if (fdset_id == -1) {
> > +            error_setg(errp, "Unable to parse fdset %s", name);
> >              errno = EINVAL;
> >              return -1;
> >          }
> >  
> >          fd = monitor_fdset_get_fd(fdset_id, flags);
> >          if (fd < 0) {
> > +            error_setg_errno(errp, -fd, "Unable acquire FD for %s flags %x",
> > +                             name, flags);
> >              errno = -fd;
> >              return -1;
> >          }
> >  
> >          dupfd = qemu_dup_flags(fd, flags);
> >          if (dupfd == -1) {
> > +            error_setg_errno(errp, errno, "Unable dup FD for %s flags %x",
> > +                             name, flags);
> >              return -1;
> >          }
> >  
> >          ret = monitor_fdset_dup_fd_add(fdset_id, dupfd);
> >          if (ret == -1) {
> >              close(dupfd);
> > +            error_setg(errp, "Unable save FD for %s flags %x",
> > +                       name, flags);
> >              errno = EINVAL;
> >              return -1;
> >          }
> > @@ -324,11 +332,7 @@ int qemu_open(const char *name, int flags, ...)
> >  #endif
> >  
> >      if (flags & O_CREAT) {
> > -        va_list ap;
> > -
> > -        va_start(ap, flags);
> >          mode = va_arg(ap, int);
> > -        va_end(ap);
> >      }
> >  
> >  #ifdef O_CLOEXEC
> > @@ -340,25 +344,64 @@ int qemu_open(const char *name, int flags, ...)
> >      }
> >  #endif
> >  
> > +    if (ret == -1) {
> > +        const char *action = "open";
> > +        if (flags & O_CREAT) {
> > +            action = "create";
> > +        }
> >  #ifdef O_DIRECT
> > -    if (ret == -1 && errno == EINVAL && (flags & O_DIRECT)) {
> > -        int newflags = flags & ~O_DIRECT;
> > +        if (errno == EINVAL && (flags & O_DIRECT)) {
> > +            int newflags = flags & ~O_DIRECT;
> >  # ifdef O_CLOEXEC
> > -        ret = open(name, newflags | O_CLOEXEC, mode);
> > +            ret = open(name, newflags | O_CLOEXEC, mode);
> >  # else
> > -        ret = open(name, newflags, mode);
> > +            ret = open(name, newflags, mode);
> >  # endif
> > -        if (ret != -1) {
> > -            close(ret);
> > -            error_report("file system does not support O_DIRECT");
> > -            errno = EINVAL;
> > +            if (ret != -1) {
> > +                close(ret);
> > +                error_setg(errp, "Unable to %s '%s' flags 0x%x: "
> > +                           "filesystem does not support O_DIRECT",
> > +                           action, name, flags);
> > +                if (!errp) {
> 
> If the caller ignores errors, ...
> 
> > +                    error_report("file system does not support O_DIRECT");
> 
> ... we report this error to stderr (but not any of the other ones).
> This is weird.  I figure you do it here to reproduce the weirdness of
> qemu_open() before the patch.  Goes back to
> 
>     commit a5813077aac7865f69b7ee46a594f3705429f7cd
>     Author: Stefan Hajnoczi <stefanha@redhat.com>
>     Date:   Thu Aug 22 11:29:03 2013 +0200
> 
>         osdep: warn if open(O_DIRECT) on fails with EINVAL
> 
>         Print a warning when opening a file O_DIRECT fails with EINVAL.  This
>         saves users a lot of time trying to figure out the EINVAL error, which
>         is typical when attempting to open a file O_DIRECT on Linux tmpfs.
> 
>         Reported-by: Deepak C Shetty <deepakcs@linux.vnet.ibm.com>
>         Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
>         Reviewed-by: Eric Blake <eblake@redhat.com>
> 
> The message isn't phrased as a warning, though.  Should it use
> warn_report()?  Stefan?

I was really in two minds as to whether to keep this error_report or
not. It depends depends on whether any other callers of qemu_open
still need it. In fact if nothing outside the block layer uses O_DIRECT
then I think we can remove the error_report line.


> > +int qemu_open_err(const char *name, int flags, Error **errp, ...)
> > +{
> > +    va_list ap;
> > +    int rv;
> > +
> > +    va_start(ap, errp);
> > +    rv = qemu_openv(name, flags, errp, ap);
> > +    va_end(ap);
> > +
> > +    return rv;
> > +}
> > +
> > +int qemu_open(const char *name, int flags, ...)
> > +{
> > +    va_list ap;
> > +    int rv;
> > +
> > +    va_start(ap, flags);
> > +    rv = qemu_openv(name, flags, NULL, ap);
> > +    va_end(ap);
> > +
> > +    return rv;
> > +}
> 
> I'd rename this to qemu_open_with_bad_error_messages().

My goal was to avoid a big bang conversion of all callers.

> 
> For better ones, callers can use
> 
>     if (qemu_open_err(name, flags, &err) < 0) {
>         error_report_err(err);
>         ...
>     }
> 
> or, where the error is fatal
>     
>     qemu_open_err(name, flags, &error_fatal);
> 
> If you prefer not to rename it now, please add a comment why it should
> not be used in new code, and existing uses should be converted.
> 
> If you rename, call the new one qemu_open().

Maybe it is better to rename upfront though, instead of waiting till
everything uses the qemu_open_err and then renaming back to qemu_open.

Regards,
Daniel
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